diff --git a/backend/src/main/java/de/assecutor/votianlt/model/invoices/CustomerInvoice.java b/backend/src/main/java/de/assecutor/votianlt/model/invoices/CustomerInvoice.java
index f919d53..11283dc 100644
--- a/backend/src/main/java/de/assecutor/votianlt/model/invoices/CustomerInvoice.java
+++ b/backend/src/main/java/de/assecutor/votianlt/model/invoices/CustomerInvoice.java
@@ -66,6 +66,7 @@ public class CustomerInvoice {
     private String recipientCity;
     private String recipientCountry;
     private String recipientVatId; // USt-IdNr. des Empfängers (falls vorhanden)
+    private String recipientEmail; // E-Mail für den Rechnungsversand
 
     // Rechnungsdetails
     private String description; // Beschreibung der Leistung
@@ -274,6 +275,14 @@ public class CustomerInvoice {
         this.recipientVatId = recipientVatId;
     }
 
+    public String getRecipientEmail() {
+        return recipientEmail;
+    }
+
+    public void setRecipientEmail(String recipientEmail) {
+        this.recipientEmail = recipientEmail;
+    }
+
     public String getDescription() {
         return description;
     }
diff --git a/backend/src/main/java/de/assecutor/votianlt/pages/view/CreateInvoiceView.java b/backend/src/main/java/de/assecutor/votianlt/pages/view/CreateInvoiceView.java
index 68208f9..4f2d9c7 100644
--- a/backend/src/main/java/de/assecutor/votianlt/pages/view/CreateInvoiceView.java
+++ b/backend/src/main/java/de/assecutor/votianlt/pages/view/CreateInvoiceView.java
@@ -24,6 +24,7 @@ import de.assecutor.votianlt.model.Service;
 import de.assecutor.votianlt.model.User;
 import de.assecutor.votianlt.model.InvoiceTemplate;
 import de.assecutor.votianlt.model.invoices.CustomerInvoice;
+import de.assecutor.votianlt.model.invoices.CustomerInvoiceItem;
 import de.assecutor.votianlt.pages.base.ui.component.DialogStylingHelper;
 import de.assecutor.votianlt.pages.service.CustomerService;
 import de.assecutor.votianlt.pages.service.UserInvoiceDataService;
@@ -586,6 +587,14 @@ public class CreateInvoiceView extends VerticalLayout implements HasUrlParameter
             invoice.setVatAmount(vatAmount);
             invoice.setTotalAmount(totalAmount);
 
+            // Pflichtangaben nach §14 UStG: Leistungsdatum, Absender, Empfänger und
+            // Positionen — auch Grundlage der ZUGFeRD-Metadaten für die E-Rechnung.
+            invoice.setDeliveryDate(currentJob.getDeliveryDate() != null ? currentJob.getDeliveryDate()
+                    : java.time.LocalDate.now());
+            applySenderData(invoice, user);
+            applyRecipientData(invoice);
+            invoice.setItems(buildInvoiceItems(vatRate));
+
             invoice.setPdfData(pdfBytes);
 
             // Finalisierung mit Audit-Eintrag und Eindeutigkeitsprüfung der Rechnungsnummer (R-07/R-11/R-36).
@@ -609,6 +618,105 @@ public class CreateInvoiceView extends VerticalLayout implements HasUrlParameter
         }
     }
 
+    /**
+     * Absenderdaten aus dem Nutzerprofil und den Rechnungs-Stammdaten
+     * (USt-IdNr./Steuernummer, Bankverbindung, Zahlungsbedingungen) übernehmen.
+     */
+    private void applySenderData(CustomerInvoice invoice, User user) {
+        invoice.setSenderName(firstNonBlank(user.getCompany(),
+                (safe(user.getFirstname()) + " " + safe(user.getName())).trim()));
+        invoice.setSenderAddress((safe(user.getStreet()) + " " + safe(user.getHouseNumber())).trim());
+        invoice.setSenderPostcode(safe(user.getZip()));
+        invoice.setSenderCity(safe(user.getCity()));
+        invoice.setSenderCountry("DE");
+        invoice.setSenderPhone(safe(user.getPhone()));
+        invoice.setSenderEmail(safe(user.getEmail()));
+
+        userInvoiceDataService.findByUserId(user.getId()).ifPresent(invoiceData -> {
+            invoice.setSenderVatId(safe(invoiceData.getUstId()));
+            invoice.setSenderTaxNumber(safe(invoiceData.getTaxNumber()));
+            invoice.setIban(safe(invoiceData.getIban()));
+            invoice.setBankAccount(safe(invoiceData.getBankName()));
+            invoice.setPaymentTerms(safe(invoiceData.getPaymentTerms()));
+        });
+        if (invoice.getPaymentDueDate() == null) {
+            invoice.setPaymentDueDate(invoice.getInvoiceDate().plusDays(14));
+        }
+    }
+
+    /**
+     * Empfängerdaten aus der Kundenauswahl des Auftrags übernehmen; die volle
+     * Anschrift und E-Mail kommen aus dem passenden Adressbuch-Eintrag.
+     */
+    private void applyRecipientData(CustomerInvoice invoice) {
+        String customerSelection = currentJob.getCustomerSelection();
+        if (customerSelection == null || customerSelection.isBlank()) {
+            return;
+        }
+        // Format: "Firmenname | Vorname Nachname"
+        String[] parts = customerSelection.split("\\|");
+        String companyName = parts.length > 0 ? parts[0].trim() : "";
+        String contactName = parts.length > 1 ? parts[1].trim() : "";
+
+        invoice.setRecipientCompany(companyName);
+        invoice.setRecipientName(firstNonBlank(contactName, companyName));
+
+        Customer matchedCustomer = customerService.findAllForCurrentOwner().stream()
+                .filter(c -> companyName.equalsIgnoreCase(c.getCompanyName())).findFirst().orElse(null);
+        if (matchedCustomer != null) {
+            invoice.setRecipientAddress(
+                    (safe(matchedCustomer.getStreet()) + " " + safe(matchedCustomer.getHouseNumber())).trim());
+            invoice.setRecipientPostcode(safe(matchedCustomer.getZip()));
+            invoice.setRecipientCity(safe(matchedCustomer.getCity()));
+            invoice.setRecipientCountry("DE");
+            invoice.setRecipientEmail(safe(matchedCustomer.getMail()));
+        }
+    }
+
+    /**
+     * Rechnungspositionen aus den ausgewählten Leistungen aufbauen — mit
+     * denselben Mengen-/Preisregeln wie {@link #calculateNetAmount()}, damit
+     * die Positionssumme exakt zum Rechnungs-Netto passt.
+     */
+    private List<CustomerInvoiceItem> buildInvoiceItems(BigDecimal vatRate) {
+        List<CustomerInvoiceItem> items = new ArrayList<>();
+        for (ServiceRow row : getSelectedServices()) {
+            Service service = row.getService();
+            BigDecimal quantity = null;
+            BigDecimal unitPrice = null;
+            String unit = null;
+            if (service.getCalculationBasis() == Service.CalculationBasis.FLAT_RATE && service.getPrice() != null) {
+                quantity = BigDecimal.ONE;
+                unitPrice = service.getPrice();
+                unit = "pauschal";
+            } else if (service.getCalculationBasis() == Service.CalculationBasis.DISTANCE
+                    && service.getPricePerKilometer() != null && getRouteDistanceKm(row.getSelection()) != null) {
+                quantity = BigDecimal.valueOf(getRouteDistanceKm(row.getSelection()));
+                unitPrice = service.getPricePerKilometer();
+                unit = "km";
+            } else if (service.getCalculationBasis() == Service.CalculationBasis.TIME
+                    && service.getPricePer15Minutes() != null && getTimeIn15MinUnits(row.getSelection()) != null) {
+                quantity = new BigDecimal(getTimeIn15MinUnits(row.getSelection()));
+                unitPrice = service.getPricePer15Minutes();
+                unit = "x 15 Min.";
+            }
+            if (quantity == null || quantity.signum() <= 0 || unitPrice == null) {
+                continue;
+            }
+            items.add(new CustomerInvoiceItem(quantity, unit, service.getName(), unitPrice, vatRate));
+        }
+        return items;
+    }
+
+    private String firstNonBlank(String... values) {
+        for (String value : values) {
+            if (value != null && !value.isBlank()) {
+                return value;
+            }
+        }
+        return "";
+    }
+
     /**
      * Generates an invoice PDF from the template with actual job data.
      */
diff --git a/backend/src/main/java/de/assecutor/votianlt/pages/view/EditProfileView.java b/backend/src/main/java/de/assecutor/votianlt/pages/view/EditProfileView.java
index f5833d1..6d421e4 100644
--- a/backend/src/main/java/de/assecutor/votianlt/pages/view/EditProfileView.java
+++ b/backend/src/main/java/de/assecutor/votianlt/pages/view/EditProfileView.java
@@ -372,6 +372,24 @@ public class EditProfileView extends HorizontalLayout implements HasDynamicTitle
         billingHeaderLayout.setAlignItems(FlexComponent.Alignment.BASELINE);
         billingTab.add(billingHeaderLayout);
 
+        // Steuer- und Bankdaten: Pflichtangaben nach §14 UStG bzw. für die
+        // ZUGFeRD-E-Rechnung (Absender-USt-IdNr./Steuernummer, IBAN)
+        ustIdField.setLabel(getTranslation("profile.billing.ustid"));
+        ustIdField.setPlaceholder("DE123456789");
+        ustIdField.addBlurListener(e -> saveInvoiceData());
+        taxNumberField.setLabel(getTranslation("profile.billing.taxnumber"));
+        taxNumberField.addBlurListener(e -> saveInvoiceData());
+        bankNameField.setLabel(getTranslation("profile.billing.bankname"));
+        bankNameField.addBlurListener(e -> saveInvoiceData());
+        ibanField.setLabel(getTranslation("profile.billing.iban"));
+        ibanField.setPlaceholder("DE00 0000 0000 0000 0000 00");
+        ibanField.addBlurListener(e -> saveInvoiceData());
+
+        HorizontalLayout billingTaxLayout = new HorizontalLayout(ustIdField, taxNumberField, bankNameField, ibanField);
+        billingTaxLayout.setSpacing(true);
+        billingTaxLayout.setAlignItems(FlexComponent.Alignment.BASELINE);
+        billingTab.add(billingTaxLayout);
+
         // Hauptlayout: Links (Templates) | Mitte (Canvas) | Rechts (Eigenschaften)
         final HorizontalLayout mainLayout = new HorizontalLayout();
         mainLayout.setWidthFull();
diff --git a/backend/src/main/java/de/assecutor/votianlt/pages/view/InvoicesView.java b/backend/src/main/java/de/assecutor/votianlt/pages/view/InvoicesView.java
index d173d45..5350aea 100644
--- a/backend/src/main/java/de/assecutor/votianlt/pages/view/InvoicesView.java
+++ b/backend/src/main/java/de/assecutor/votianlt/pages/view/InvoicesView.java
@@ -33,11 +33,15 @@ import de.assecutor.votianlt.repository.CustomerInvoiceRepository;
 import de.assecutor.votianlt.repository.UserRepository;
 import de.assecutor.votianlt.security.SecurityService;
 import de.assecutor.votianlt.service.CustomerInvoiceService;
+import de.assecutor.votianlt.service.EmailService;
 import de.assecutor.votianlt.service.InvoiceExportService;
 import de.assecutor.votianlt.service.InvoiceLifecycleException;
 import de.assecutor.votianlt.service.InvoiceLifecycleService;
 import de.assecutor.votianlt.service.InvoicePermissionService;
+import de.assecutor.votianlt.service.PdfToolService;
+import de.assecutor.votianlt.service.UserInvoiceZugferdService;
 import jakarta.annotation.security.RolesAllowed;
+import lombok.extern.slf4j.Slf4j;
 
 import java.io.ByteArrayInputStream;
 import java.time.LocalDate;
@@ -49,6 +53,7 @@ import java.util.Optional;
 
 @Route(value = "invoices", layout = de.assecutor.votianlt.pages.base.ui.view.MainLayout.class)
 @RolesAllowed({ "USER", "ADMIN" })
+@Slf4j
 public class InvoicesView extends VerticalLayout implements HasDynamicTitle {
 
     private static final DateTimeFormatter DATE_TIME_FMT = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm",
@@ -63,12 +68,15 @@ public class InvoicesView extends VerticalLayout implements HasDynamicTitle {
     private final InvoicePermissionService invoicePermissionService;
     private final UserInvoiceDataService userInvoiceDataService;
     private final UserRepository userRepository;
+    private final UserInvoiceZugferdService userInvoiceZugferdService;
+    private final EmailService emailService;
 
     public InvoicesView(CustomerInvoiceRepository customerInvoiceRepository, SecurityService securityService,
             InvoiceLifecycleService invoiceLifecycleService, CustomerInvoiceService customerInvoiceService,
             InvoiceExportService invoiceExportService, InvoicePermissionService invoicePermissionService,
             UserInvoiceDataService userInvoiceDataService,
-            UserRepository userRepository) {
+            UserRepository userRepository, UserInvoiceZugferdService userInvoiceZugferdService,
+            EmailService emailService) {
         this.customerInvoiceRepository = customerInvoiceRepository;
         this.securityService = securityService;
         this.invoiceLifecycleService = invoiceLifecycleService;
@@ -77,6 +85,8 @@ public class InvoicesView extends VerticalLayout implements HasDynamicTitle {
         this.invoicePermissionService = invoicePermissionService;
         this.userInvoiceDataService = userInvoiceDataService;
         this.userRepository = userRepository;
+        this.userInvoiceZugferdService = userInvoiceZugferdService;
+        this.emailService = emailService;
 
         setSizeFull();
         setPadding(true);
@@ -201,6 +211,22 @@ public class InvoicesView extends VerticalLayout implements HasDynamicTitle {
             actions.add(sentBtn);
         }
 
+        // E-Rechnung (ZUGFeRD) über das externe PDF Tool — analog zu den
+        // System-Rechnungen der Admin-Seite
+        if (type == InvoiceType.INVOICE && invoice.getPdfData() != null && invoice.getPdfData().length > 0) {
+            Button zugferdBtn = new Button(getTranslation("invoices.action.zugferd"),
+                    e -> downloadZugferdZip(invoice));
+            zugferdBtn.addThemeVariants(ButtonVariant.LUMO_TERTIARY, ButtonVariant.LUMO_SMALL);
+            actions.add(zugferdBtn);
+
+            if (isLiveInvoice && invoicePermissionService.canMarkAsSent(currentUser)) {
+                Button sendBtn = new Button(getTranslation("invoices.action.sendinvoice"),
+                        e -> sendAsEInvoice(invoice));
+                sendBtn.addThemeVariants(ButtonVariant.LUMO_SMALL, ButtonVariant.LUMO_PRIMARY);
+                actions.add(sendBtn);
+            }
+        }
+
         if (isLiveInvoice) {
             if (invoicePermissionService.canCorrect(currentUser)) {
                 Button correctBtn = new Button(getTranslation("invoices.action.correct"),
@@ -318,6 +344,91 @@ public class InvoicesView extends VerticalLayout implements HasDynamicTitle {
         }
     }
 
+    /**
+     * Wandelt die Rechnung über das externe PDF Tool in eine signierte
+     * ZUGFeRD-E-Rechnung um und bietet das ZIP (PDF/A-3, factur-x.xml,
+     * Prüfbericht) als Download an.
+     */
+    private void downloadZugferdZip(CustomerInvoice invoice) {
+        try {
+            PdfToolService.SignedInvoice signed = userInvoiceZugferdService.sign(invoice);
+            triggerZipDownload(signed.zip(), signed.fileName());
+            if (signed.valid()) {
+                Notification.show(getTranslation("invoices.notification.zugferd.created", invoice.getInvoiceNumber()),
+                        5000, Notification.Position.BOTTOM_END);
+            } else {
+                Notification.show(getTranslation("invoices.notification.zugferd.invalid"), 7000,
+                        Notification.Position.MIDDLE);
+            }
+        } catch (Exception ex) {
+            log.error("Fehler beim Erstellen der ZUGFeRD-E-Rechnung {}: {}", invoice.getInvoiceNumber(),
+                    ex.getMessage(), ex);
+            Notification.show(getTranslation("invoices.notification.zugferd.error", ex.getMessage()), 7000,
+                    Notification.Position.MIDDLE);
+        }
+    }
+
+    /**
+     * Versendet die Rechnung als signierte ZUGFeRD-E-Rechnung (ZIP) per E-Mail
+     * an den Kunden. Besteht die Rechnung die Validierung nicht (HTTP 422 des
+     * PDF Tools), wird der Versand abgebrochen — wie beim Sammelversand der
+     * System-Rechnungen. Nach erfolgreichem Versand wird der Status auf
+     * "Versendet" gesetzt.
+     */
+    private void sendAsEInvoice(CustomerInvoice invoice) {
+        String recipientEmail = invoice.getRecipientEmail();
+        if (recipientEmail == null || recipientEmail.isBlank()) {
+            Notification.show(getTranslation("invoices.notification.email.missing"), 6000,
+                    Notification.Position.MIDDLE);
+            return;
+        }
+        try {
+            invoicePermissionService.requireSend(invoicePermissionService.currentUser());
+
+            PdfToolService.SignedInvoice signed = userInvoiceZugferdService.sign(invoice);
+            if (!signed.valid()) {
+                log.warn("Versand der Rechnung {} abgebrochen, ZUGFeRD-Validierung fehlgeschlagen",
+                        invoice.getInvoiceNumber());
+                Notification.show(
+                        getTranslation("invoices.notification.zugferd.invalidsend", invoice.getInvoiceNumber()), 7000,
+                        Notification.Position.MIDDLE);
+                return;
+            }
+
+            emailService.sendEmailWithAttachment(recipientEmail,
+                    getTranslation("invoices.mail.subject", invoice.getInvoiceNumber()),
+                    getTranslation("invoices.mail.body", invoice.getInvoiceNumber(),
+                            firstNonBlank(invoice.getSenderName(), "")),
+                    signed.zip(), signed.fileName());
+
+            if (invoice.getStatus() == InvoiceStatus.ISSUED) {
+                invoiceLifecycleService.markAsSent(invoice.getId(),
+                        "Als E-Rechnung per E-Mail versendet an " + recipientEmail);
+            }
+            Notification.show(
+                    getTranslation("invoices.notification.emailsent", invoice.getInvoiceNumber(), recipientEmail),
+                    5000, Notification.Position.BOTTOM_END);
+            loadInvoices();
+        } catch (InvoiceLifecycleException ex) {
+            Notification.show(ex.getMessage(), 6000, Notification.Position.MIDDLE);
+        } catch (Exception ex) {
+            log.error("Fehler beim Versand der Rechnung {} an {}: {}", invoice.getInvoiceNumber(), recipientEmail,
+                    ex.getMessage(), ex);
+            Notification.show(getTranslation("invoices.notification.zugferd.error", ex.getMessage()), 7000,
+                    Notification.Position.MIDDLE);
+        }
+    }
+
+    /** Bietet die ZIP-Bytes als Browser-Download an. */
+    private void triggerZipDownload(byte[] zip, String fileName) {
+        StreamResource resource = new StreamResource(fileName, () -> new ByteArrayInputStream(zip));
+        resource.setContentType("application/zip");
+        resource.setCacheTime(0);
+        StreamRegistration registration = UI.getCurrent().getSession().getResourceRegistry()
+                .registerResource(resource);
+        UI.getCurrent().getPage().open(registration.getResourceUri().toString());
+    }
+
     private void markAsSent(CustomerInvoice invoice) {
         try {
             invoicePermissionService.requireSend(invoicePermissionService.currentUser());
diff --git a/backend/src/main/java/de/assecutor/votianlt/service/UserInvoiceZugferdService.java b/backend/src/main/java/de/assecutor/votianlt/service/UserInvoiceZugferdService.java
new file mode 100644
index 0000000..b3fba36
--- /dev/null
+++ b/backend/src/main/java/de/assecutor/votianlt/service/UserInvoiceZugferdService.java
@@ -0,0 +1,122 @@
+package de.assecutor.votianlt.service;
+
+import de.assecutor.votianlt.model.invoices.CustomerInvoice;
+import de.assecutor.votianlt.model.invoices.CustomerInvoiceItem;
+import org.springframework.stereotype.Service;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Wandelt Nutzer-Rechnungen (Rechnungen der Systemnutzer an ihre eigenen
+ * Kunden) über das externe PDF Tool in signierte ZUGFeRD-E-Rechnungen um —
+ * dasselbe Verfahren, das {@code AdminCreateInvoicesView} für die
+ * System-Rechnungen verwendet. Die EN16931-Metadaten werden vollständig aus
+ * der persistierten {@link CustomerInvoice} aufgebaut (Absender, Empfänger,
+ * Positionen), die beim Erstellen der Rechnung in {@code CreateInvoiceView}
+ * befüllt werden.
+ */
+@Service
+public class UserInvoiceZugferdService {
+
+    private final PdfToolService pdfToolService;
+
+    public UserInvoiceZugferdService(PdfToolService pdfToolService) {
+        this.pdfToolService = pdfToolService;
+    }
+
+    /**
+     * Signiert die Rechnung über das PDF Tool. Wirft eine
+     * {@link IllegalStateException} mit verständlicher Meldung, wenn der
+     * Rechnung Daten fehlen, die für eine EN16931-E-Rechnung zwingend sind.
+     */
+    public PdfToolService.SignedInvoice sign(CustomerInvoice invoice) throws Exception {
+        if (invoice.getPdfData() == null || invoice.getPdfData().length == 0) {
+            throw new IllegalStateException("Für diese Rechnung ist kein PDF gespeichert.");
+        }
+        return pdfToolService.signInvoice(invoice.getPdfData(), buildMetadata(invoice));
+    }
+
+    private PdfToolService.InvoiceMetadata buildMetadata(CustomerInvoice invoice) {
+        if (isBlank(invoice.getSenderName()) || isBlank(invoice.getRecipientName())) {
+            throw new IllegalStateException(
+                    "Absender- oder Empfängerdaten fehlen — diese Rechnung wurde vor der E-Rechnungs-Umstellung "
+                            + "erstellt und kann nicht als E-Rechnung aufbereitet werden.");
+        }
+
+        PdfToolService.Party sender = new PdfToolService.Party(invoice.getSenderName(),
+                safe(invoice.getSenderAddress()), safe(invoice.getSenderPostcode()), safe(invoice.getSenderCity()),
+                firstNonBlank(invoice.getSenderCountry(), "DE"), blankToNull(invoice.getSenderVatId()),
+                safe(invoice.getSenderEmail()), safe(invoice.getSenderPhone()));
+
+        PdfToolService.Party recipient = new PdfToolService.Party(
+                firstNonBlank(invoice.getRecipientCompany(), invoice.getRecipientName()),
+                safe(invoice.getRecipientAddress()), safe(invoice.getRecipientPostcode()),
+                safe(invoice.getRecipientCity()), firstNonBlank(invoice.getRecipientCountry(), "DE"),
+                blankToNull(invoice.getRecipientVatId()), safe(invoice.getRecipientEmail()), null);
+
+        List<PdfToolService.LineItem> items = buildLineItems(invoice);
+        if (items.isEmpty()) {
+            throw new IllegalStateException("Die Rechnung enthält keine Positionen mit Betrag.");
+        }
+
+        LocalDate issueDate = invoice.getInvoiceDate() != null ? invoice.getInvoiceDate() : LocalDate.now();
+        LocalDate deliveryDate = invoice.getDeliveryDate() != null ? invoice.getDeliveryDate() : issueDate;
+        LocalDate dueDate = invoice.getPaymentDueDate() != null ? invoice.getPaymentDueDate() : issueDate.plusDays(14);
+
+        return new PdfToolService.InvoiceMetadata(invoice.getInvoiceNumber(), issueDate, deliveryDate, dueDate, "EUR",
+                safe(invoice.getPaymentTerms()), null, blankToNull(invoice.getIban()), blankToNull(invoice.getBic()),
+                sender, recipient, items);
+    }
+
+    private List<PdfToolService.LineItem> buildLineItems(CustomerInvoice invoice) {
+        BigDecimal vatPercent = invoice.getVatRate() != null
+                ? invoice.getVatRate().multiply(new BigDecimal("100")).setScale(0, RoundingMode.HALF_UP)
+                : new BigDecimal("19");
+
+        List<PdfToolService.LineItem> items = new ArrayList<>();
+        if (invoice.getItems() != null) {
+            for (CustomerInvoiceItem item : invoice.getItems()) {
+                if (item == null || item.getQuantity() == null || item.getUnitPrice() == null) {
+                    continue;
+                }
+                BigDecimal itemVatPercent = item.getVatRate() != null
+                        ? item.getVatRate().multiply(new BigDecimal("100")).setScale(0, RoundingMode.HALF_UP)
+                        : vatPercent;
+                items.add(new PdfToolService.LineItem(safe(item.getDescription()), item.getQuantity(),
+                        item.getUnitPrice(), itemVatPercent));
+            }
+        }
+        // Ältere Rechnungen ohne Positionsliste: eine Sammelposition aus dem
+        // Rechnungs-Netto, damit sie trotzdem als E-Rechnung versendbar bleiben.
+        if (items.isEmpty() && invoice.getNetAmount() != null && invoice.getNetAmount().signum() > 0) {
+            items.add(new PdfToolService.LineItem(firstNonBlank(invoice.getDescription(), "Leistung gemäß Rechnung"),
+                    BigDecimal.ONE, invoice.getNetAmount(), vatPercent));
+        }
+        return items;
+    }
+
+    private String safe(String value) {
+        return value != null ? value : "";
+    }
+
+    private String blankToNull(String value) {
+        return value == null || value.isBlank() ? null : value;
+    }
+
+    private String firstNonBlank(String... values) {
+        for (String value : values) {
+            if (value != null && !value.isBlank()) {
+                return value;
+            }
+        }
+        return "";
+    }
+
+    private boolean isBlank(String value) {
+        return value == null || value.isBlank();
+    }
+}
diff --git a/backend/src/main/resources/messages_de.properties b/backend/src/main/resources/messages_de.properties
index af7f288..9fc4edf 100644
--- a/backend/src/main/resources/messages_de.properties
+++ b/backend/src/main/resources/messages_de.properties
@@ -1156,3 +1156,19 @@ admincreateinvoices.notification.zugferd.nopositions=Keine abrechenbaren Positio
 admincreateinvoices.notification.zugferd.batcherror=E-Rechnung {0} konnte nicht erstellt werden, es wurden keine Rechnungen versendet: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Validierung fehlgeschlagen für: {0}. Es wurden keine Rechnungen versendet.
 admincreateinvoices.notification.zip.combined.error=Fehler beim Erstellen der Sammel-ZIP-Datei: {0}
+
+# E-Rechnung (ZUGFeRD) für Nutzer-Rechnungen an ihre Kunden
+invoices.action.zugferd=E-Rechnung (ZIP)
+invoices.action.sendinvoice=Per E-Mail senden
+invoices.notification.zugferd.created=E-Rechnung {0} erstellt
+invoices.notification.zugferd.invalid=E-Rechnung erstellt, aber die Validierung ist fehlgeschlagen. Details im Prüfbericht in der ZIP-Datei.
+invoices.notification.zugferd.invalidsend=Versand abgebrochen: Die Validierung der E-Rechnung {0} ist fehlgeschlagen.
+invoices.notification.zugferd.error=Fehler bei der E-Rechnung: {0}
+invoices.notification.email.missing=Für den Rechnungsempfänger ist keine E-Mail-Adresse hinterlegt.
+invoices.notification.emailsent=Rechnung {0} wurde als E-Rechnung an {1} versendet.
+invoices.mail.subject=Ihre Rechnung {0}
+invoices.mail.body=Sehr geehrte Damen und Herren,\n\nanbei erhalten Sie Ihre Rechnung {0} als E-Rechnung (ZIP mit PDF und Rechnungsdaten).\n\nMit freundlichen Grüßen\n{1}
+profile.billing.ustid=USt-IdNr.
+profile.billing.taxnumber=Steuernummer
+profile.billing.bankname=Bank
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_ee.properties b/backend/src/main/resources/messages_ee.properties
index 01ba996..0d81fac 100644
--- a/backend/src/main/resources/messages_ee.properties
+++ b/backend/src/main/resources/messages_ee.properties
@@ -986,3 +986,19 @@ admincreateinvoices.notification.zugferd.nopositions=E-arve jaoks puuduvad arvel
 admincreateinvoices.notification.zugferd.batcherror=E-arvet {0} ei õnnestunud luua, ühtegi arvet ei saadetud: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Valideerimine ebaõnnestus: {0}. Ühtegi arvet ei saadetud.
 admincreateinvoices.notification.zip.combined.error=Viga koond-ZIP-faili loomisel: {0}
+
+# E-arve (ZUGFeRD) kasutajate arvetele nende klientidele
+invoices.action.zugferd=E-arve (ZIP)
+invoices.action.sendinvoice=Saada e-postiga
+invoices.notification.zugferd.created=E-arve {0} loodud
+invoices.notification.zugferd.invalid=E-arve loodi, kuid valideerimine ebaõnnestus. Vaadake kontrolliaruannet ZIP-failis.
+invoices.notification.zugferd.invalidsend=Saatmine katkestati: e-arve {0} valideerimine ebaõnnestus.
+invoices.notification.zugferd.error=E-arve viga: {0}
+invoices.notification.email.missing=Arve saajale pole e-posti aadressi salvestatud.
+invoices.notification.emailsent=Arve {0} saadeti e-arvena aadressile {1}.
+invoices.mail.subject=Teie arve {0}
+invoices.mail.body=Lugupeetud klient,\n\nmanuses on Teie arve {0} e-arvena (ZIP koos PDF-i ja arveandmetega).\n\nLugupidamisega\n{1}
+profile.billing.ustid=KMKR nr
+profile.billing.taxnumber=Maksunumber
+profile.billing.bankname=Pank
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_en.properties b/backend/src/main/resources/messages_en.properties
index 78c440a..12cc5cd 100644
--- a/backend/src/main/resources/messages_en.properties
+++ b/backend/src/main/resources/messages_en.properties
@@ -1156,3 +1156,19 @@ admincreateinvoices.notification.zugferd.nopositions=No billable positions avail
 admincreateinvoices.notification.zugferd.batcherror=E-invoice {0} could not be created, no invoices were sent: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Validation failed for: {0}. No invoices were sent.
 admincreateinvoices.notification.zip.combined.error=Error creating the combined ZIP file: {0}
+
+# E-invoice (ZUGFeRD) for user invoices to their customers
+invoices.action.zugferd=E-invoice (ZIP)
+invoices.action.sendinvoice=Send by email
+invoices.notification.zugferd.created=E-invoice {0} created
+invoices.notification.zugferd.invalid=E-invoice created, but validation failed. See the validation report in the ZIP file.
+invoices.notification.zugferd.invalidsend=Sending aborted: validation of e-invoice {0} failed.
+invoices.notification.zugferd.error=E-invoice error: {0}
+invoices.notification.email.missing=No email address is stored for the invoice recipient.
+invoices.notification.emailsent=Invoice {0} was sent as an e-invoice to {1}.
+invoices.mail.subject=Your invoice {0}
+invoices.mail.body=Dear Sir or Madam,\n\nPlease find attached your invoice {0} as an e-invoice (ZIP with PDF and invoice data).\n\nKind regards\n{1}
+profile.billing.ustid=VAT ID
+profile.billing.taxnumber=Tax number
+profile.billing.bankname=Bank
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_es.properties b/backend/src/main/resources/messages_es.properties
index 5356668..ce5f166 100644
--- a/backend/src/main/resources/messages_es.properties
+++ b/backend/src/main/resources/messages_es.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=No hay posiciones facturabl
 admincreateinvoices.notification.zugferd.batcherror=No se pudo crear la factura electrónica {0}, no se envió ninguna factura: {1}
 admincreateinvoices.notification.zugferd.invalidsend=La validación falló para: {0}. No se envió ninguna factura.
 admincreateinvoices.notification.zip.combined.error=Error al crear el archivo ZIP combinado: {0}
+
+# Factura electrónica (ZUGFeRD) para facturas de usuarios a sus clientes
+invoices.action.zugferd=Factura electrónica (ZIP)
+invoices.action.sendinvoice=Enviar por correo
+invoices.notification.zugferd.created=Factura electrónica {0} creada
+invoices.notification.zugferd.invalid=Factura electrónica creada, pero la validación ha fallado. Consulte el informe de validación en el archivo ZIP.
+invoices.notification.zugferd.invalidsend=Envío cancelado: la validación de la factura electrónica {0} ha fallado.
+invoices.notification.zugferd.error=Error en la factura electrónica: {0}
+invoices.notification.email.missing=No hay una dirección de correo electrónico registrada para el destinatario de la factura.
+invoices.notification.emailsent=La factura {0} se envió como factura electrónica a {1}.
+invoices.mail.subject=Su factura {0}
+invoices.mail.body=Estimados señores:\n\nAdjunto encontrará su factura {0} como factura electrónica (ZIP con PDF y datos de la factura).\n\nAtentamente\n{1}
+profile.billing.ustid=NIF-IVA
+profile.billing.taxnumber=Número fiscal
+profile.billing.bankname=Banco
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_fr.properties b/backend/src/main/resources/messages_fr.properties
index 2f0ca51..e156c13 100644
--- a/backend/src/main/resources/messages_fr.properties
+++ b/backend/src/main/resources/messages_fr.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=Aucune position facturable
 admincreateinvoices.notification.zugferd.batcherror=La facture électronique {0} n''a pas pu être créée, aucune facture n''a été envoyée : {1}
 admincreateinvoices.notification.zugferd.invalidsend=La validation a échoué pour : {0}. Aucune facture n''a été envoyée.
 admincreateinvoices.notification.zip.combined.error=Erreur lors de la création du fichier ZIP combiné : {0}
+
+# Facture électronique (ZUGFeRD) pour les factures des utilisateurs à leurs clients
+invoices.action.zugferd=Facture électronique (ZIP)
+invoices.action.sendinvoice=Envoyer par e-mail
+invoices.notification.zugferd.created=Facture électronique {0} créée
+invoices.notification.zugferd.invalid=Facture électronique créée, mais la validation a échoué. Voir le rapport de validation dans le fichier ZIP.
+invoices.notification.zugferd.invalidsend=Envoi annulé : la validation de la facture électronique {0} a échoué.
+invoices.notification.zugferd.error=Erreur de facture électronique : {0}
+invoices.notification.email.missing=Aucune adresse e-mail n'est enregistrée pour le destinataire de la facture.
+invoices.notification.emailsent=La facture {0} a été envoyée en tant que facture électronique à {1}.
+invoices.mail.subject=Votre facture {0}
+invoices.mail.body=Madame, Monsieur,\n\nVeuillez trouver ci-joint votre facture {0} sous forme de facture électronique (ZIP avec PDF et données de facturation).\n\nCordialement\n{1}
+profile.billing.ustid=N° TVA intracommunautaire
+profile.billing.taxnumber=Numéro fiscal
+profile.billing.bankname=Banque
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_lt.properties b/backend/src/main/resources/messages_lt.properties
index cbde87a..dc43c34 100644
--- a/backend/src/main/resources/messages_lt.properties
+++ b/backend/src/main/resources/messages_lt.properties
@@ -1089,3 +1089,19 @@ admincreateinvoices.notification.zugferd.nopositions=E. sąskaitai nėra apmokes
 admincreateinvoices.notification.zugferd.batcherror=Nepavyko sukurti e. sąskaitos {0}, sąskaitos nebuvo išsiųstos: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Patikrinimas nepavyko: {0}. Sąskaitos nebuvo išsiųstos.
 admincreateinvoices.notification.zip.combined.error=Klaida kuriant bendrą ZIP failą: {0}
+
+# E. sąskaita (ZUGFeRD) naudotojų sąskaitoms jų klientams
+invoices.action.zugferd=E. sąskaita (ZIP)
+invoices.action.sendinvoice=Siųsti el. paštu
+invoices.notification.zugferd.created=E. sąskaita {0} sukurta
+invoices.notification.zugferd.invalid=E. sąskaita sukurta, bet patikra nepavyko. Žr. patikros ataskaitą ZIP faile.
+invoices.notification.zugferd.invalidsend=Siuntimas nutrauktas: e. sąskaitos {0} patikra nepavyko.
+invoices.notification.zugferd.error=E. sąskaitos klaida: {0}
+invoices.notification.email.missing=Sąskaitos gavėjui nėra išsaugoto el. pašto adreso.
+invoices.notification.emailsent=Sąskaita {0} išsiųsta kaip e. sąskaita adresu {1}.
+invoices.mail.subject=Jūsų sąskaita {0}
+invoices.mail.body=Gerbiamieji,\n\npridedame Jūsų sąskaitą {0} kaip e. sąskaitą (ZIP su PDF ir sąskaitos duomenimis).\n\nPagarbiai\n{1}
+profile.billing.ustid=PVM mokėtojo kodas
+profile.billing.taxnumber=Mokesčių mokėtojo numeris
+profile.billing.bankname=Bankas
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_lv.properties b/backend/src/main/resources/messages_lv.properties
index 6ecd6d0..c997e81 100644
--- a/backend/src/main/resources/messages_lv.properties
+++ b/backend/src/main/resources/messages_lv.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=E-rēķinam nav pieejamu no
 admincreateinvoices.notification.zugferd.batcherror=Neizdevās izveidot e-rēķinu {0}, rēķini netika nosūtīti: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Validācija neizdevās: {0}. Rēķini netika nosūtīti.
 admincreateinvoices.notification.zip.combined.error=Kļūda, veidojot apvienoto ZIP failu: {0}
+
+# E-rēķins (ZUGFeRD) lietotāju rēķiniem viņu klientiem
+invoices.action.zugferd=E-rēķins (ZIP)
+invoices.action.sendinvoice=Sūtīt pa e-pastu
+invoices.notification.zugferd.created=E-rēķins {0} izveidots
+invoices.notification.zugferd.invalid=E-rēķins izveidots, bet validācija neizdevās. Skatiet pārbaudes atskaiti ZIP failā.
+invoices.notification.zugferd.invalidsend=Sūtīšana pārtraukta: e-rēķina {0} validācija neizdevās.
+invoices.notification.zugferd.error=E-rēķina kļūda: {0}
+invoices.notification.email.missing=Rēķina saņēmējam nav saglabāta e-pasta adrese.
+invoices.notification.emailsent=Rēķins {0} nosūtīts kā e-rēķins uz {1}.
+invoices.mail.subject=Jūsu rēķins {0}
+invoices.mail.body=Cienījamie klienti!\n\nPielikumā Jūsu rēķins {0} kā e-rēķins (ZIP ar PDF un rēķina datiem).\n\nAr cieņu\n{1}
+profile.billing.ustid=PVN numurs
+profile.billing.taxnumber=Nodokļu maksātāja numurs
+profile.billing.bankname=Banka
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_pl.properties b/backend/src/main/resources/messages_pl.properties
index a3490b9..172bdec 100644
--- a/backend/src/main/resources/messages_pl.properties
+++ b/backend/src/main/resources/messages_pl.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=Brak pozycji rozliczeniowyc
 admincreateinvoices.notification.zugferd.batcherror=Nie udało się utworzyć e-faktury {0}, żadne faktury nie zostały wysłane: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Walidacja nie powiodła się dla: {0}. Żadne faktury nie zostały wysłane.
 admincreateinvoices.notification.zip.combined.error=Błąd podczas tworzenia zbiorczego pliku ZIP: {0}
+
+# E-faktura (ZUGFeRD) dla faktur użytkowników dla ich klientów
+invoices.action.zugferd=E-faktura (ZIP)
+invoices.action.sendinvoice=Wyślij e-mailem
+invoices.notification.zugferd.created=E-faktura {0} utworzona
+invoices.notification.zugferd.invalid=E-faktura została utworzona, ale walidacja nie powiodła się. Zobacz raport walidacji w pliku ZIP.
+invoices.notification.zugferd.invalidsend=Wysyłka przerwana: walidacja e-faktury {0} nie powiodła się.
+invoices.notification.zugferd.error=Błąd e-faktury: {0}
+invoices.notification.email.missing=Dla odbiorcy faktury nie zapisano adresu e-mail.
+invoices.notification.emailsent=Faktura {0} została wysłana jako e-faktura na adres {1}.
+invoices.mail.subject=Państwa faktura {0}
+invoices.mail.body=Szanowni Państwo,\n\nw załączeniu przesyłamy fakturę {0} jako e-fakturę (ZIP z plikiem PDF i danymi faktury).\n\nZ poważaniem\n{1}
+profile.billing.ustid=NIP UE
+profile.billing.taxnumber=Numer podatkowy
+profile.billing.bankname=Bank
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_ru.properties b/backend/src/main/resources/messages_ru.properties
index 933da21..6980975 100644
--- a/backend/src/main/resources/messages_ru.properties
+++ b/backend/src/main/resources/messages_ru.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=Нет позиций дл
 admincreateinvoices.notification.zugferd.batcherror=Не удалось создать электронный счёт {0}, счета не были отправлены: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Проверка не пройдена для: {0}. Счета не были отправлены.
 admincreateinvoices.notification.zip.combined.error=Ошибка при создании общего ZIP-файла: {0}
+
+# Электронный счёт (ZUGFeRD) для счетов пользователей их клиентам
+invoices.action.zugferd=Электронный счёт (ZIP)
+invoices.action.sendinvoice=Отправить по эл. почте
+invoices.notification.zugferd.created=Электронный счёт {0} создан
+invoices.notification.zugferd.invalid=Электронный счёт создан, но проверка не пройдена. См. отчёт о проверке в ZIP-файле.
+invoices.notification.zugferd.invalidsend=Отправка отменена: проверка электронного счёта {0} не пройдена.
+invoices.notification.zugferd.error=Ошибка электронного счёта: {0}
+invoices.notification.email.missing=Для получателя счёта не сохранён адрес электронной почты.
+invoices.notification.emailsent=Счёт {0} отправлен как электронный счёт на {1}.
+invoices.mail.subject=Ваш счёт {0}
+invoices.mail.body=Уважаемые дамы и господа!\n\nВо вложении Ваш счёт {0} в виде электронного счёта (ZIP с PDF и данными счёта).\n\nС уважением\n{1}
+profile.billing.ustid=Идентификатор плательщика НДС
+profile.billing.taxnumber=Налоговый номер
+profile.billing.bankname=Банк
+profile.billing.iban=IBAN
diff --git a/backend/src/main/resources/messages_tr.properties b/backend/src/main/resources/messages_tr.properties
index 8e8a94c..5ba9b85 100644
--- a/backend/src/main/resources/messages_tr.properties
+++ b/backend/src/main/resources/messages_tr.properties
@@ -1087,3 +1087,19 @@ admincreateinvoices.notification.zugferd.nopositions=E-fatura için faturalandı
 admincreateinvoices.notification.zugferd.batcherror=E-fatura {0} oluşturulamadı, hiçbir fatura gönderilmedi: {1}
 admincreateinvoices.notification.zugferd.invalidsend=Doğrulama başarısız oldu: {0}. Hiçbir fatura gönderilmedi.
 admincreateinvoices.notification.zip.combined.error=Toplu ZIP dosyası oluşturulurken hata: {0}
+
+# Kullanıcıların müşterilerine kestiği faturalar için e-fatura (ZUGFeRD)
+invoices.action.zugferd=E-fatura (ZIP)
+invoices.action.sendinvoice=E-posta ile gönder
+invoices.notification.zugferd.created=E-fatura {0} oluşturuldu
+invoices.notification.zugferd.invalid=E-fatura oluşturuldu, ancak doğrulama başarısız oldu. ZIP dosyasındaki doğrulama raporuna bakın.
+invoices.notification.zugferd.invalidsend=Gönderim iptal edildi: {0} e-faturasının doğrulaması başarısız oldu.
+invoices.notification.zugferd.error=E-fatura hatası: {0}
+invoices.notification.email.missing=Fatura alıcısı için kayıtlı bir e-posta adresi yok.
+invoices.notification.emailsent={0} numaralı fatura e-fatura olarak {1} adresine gönderildi.
+invoices.mail.subject=Faturanız {0}
+invoices.mail.body=Sayın yetkili,\n\nekte {0} numaralı faturanızı e-fatura olarak (PDF ve fatura verilerini içeren ZIP) bulabilirsiniz.\n\nSaygılarımızla\n{1}
+profile.billing.ustid=KDV kimlik no
+profile.billing.taxnumber=Vergi numarası
+profile.billing.bankname=Banka
+profile.billing.iban=IBAN
diff --git a/backend/src/test/java/de/assecutor/votianlt/service/UserInvoiceZugferdServiceTest.java b/backend/src/test/java/de/assecutor/votianlt/service/UserInvoiceZugferdServiceTest.java
new file mode 100644
index 0000000..b8c6ae1
--- /dev/null
+++ b/backend/src/test/java/de/assecutor/votianlt/service/UserInvoiceZugferdServiceTest.java
@@ -0,0 +1,161 @@
+package de.assecutor.votianlt.service;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import de.assecutor.votianlt.model.invoices.CustomerInvoice;
+import de.assecutor.votianlt.model.invoices.CustomerInvoiceItem;
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+class UserInvoiceZugferdServiceTest {
+
+    @Mock
+    private PdfToolService pdfToolService;
+
+    @Captor
+    private ArgumentCaptor<PdfToolService.InvoiceMetadata> metadataCaptor;
+
+    private UserInvoiceZugferdService service;
+
+    @BeforeEach
+    void setUp() {
+        service = new UserInvoiceZugferdService(pdfToolService);
+    }
+
+    private CustomerInvoice fullyPopulatedInvoice() {
+        CustomerInvoice invoice = new CustomerInvoice();
+        invoice.setInvoiceNumber("RE-2026-0001");
+        invoice.setInvoiceDate(LocalDate.of(2026, 7, 14));
+        invoice.setDeliveryDate(LocalDate.of(2026, 7, 10));
+        invoice.setPaymentDueDate(LocalDate.of(2026, 7, 28));
+        invoice.setSenderName("Spedition Muster GmbH");
+        invoice.setSenderAddress("Musterstraße 1");
+        invoice.setSenderPostcode("20095");
+        invoice.setSenderCity("Hamburg");
+        invoice.setSenderVatId("DE123456789");
+        invoice.setSenderEmail("info@muster.de");
+        invoice.setSenderPhone("040 123456");
+        invoice.setRecipientCompany("Kunde AG");
+        invoice.setRecipientName("Erika Beispiel");
+        invoice.setRecipientAddress("Beispielweg 2");
+        invoice.setRecipientPostcode("10115");
+        invoice.setRecipientCity("Berlin");
+        invoice.setRecipientEmail("rechnung@kunde-ag.de");
+        invoice.setVatRate(new BigDecimal("0.19"));
+        invoice.setNetAmount(new BigDecimal("100.00"));
+        invoice.setIban("DE02120300000000202051");
+        invoice.setPaymentTerms("Zahlbar innerhalb von 14 Tagen");
+        invoice.setItems(List.of(
+                new CustomerInvoiceItem(new BigDecimal("12"), "km", "Transport", new BigDecimal("5.00"),
+                        new BigDecimal("0.19")),
+                new CustomerInvoiceItem(BigDecimal.ONE, "pauschal", "Grundpreis", new BigDecimal("40.00"),
+                        new BigDecimal("0.19"))));
+        invoice.setPdfData(new byte[] { 1, 2, 3 });
+        return invoice;
+    }
+
+    @Test
+    void signBuildsMetadataFromInvoice() throws Exception {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        PdfToolService.SignedInvoice signed = new PdfToolService.SignedInvoice(new byte[] { 9 }, "re.zip", true);
+        when(pdfToolService.signInvoice(eq(invoice.getPdfData()), any())).thenReturn(signed);
+
+        PdfToolService.SignedInvoice result = service.sign(invoice);
+
+        assertThat(result).isSameAs(signed);
+        verify(pdfToolService).signInvoice(eq(invoice.getPdfData()), metadataCaptor.capture());
+        PdfToolService.InvoiceMetadata metadata = metadataCaptor.getValue();
+        assertThat(metadata.invoiceNumber()).isEqualTo("RE-2026-0001");
+        assertThat(metadata.issueDate()).isEqualTo(LocalDate.of(2026, 7, 14));
+        assertThat(metadata.deliveryDate()).isEqualTo(LocalDate.of(2026, 7, 10));
+        assertThat(metadata.dueDate()).isEqualTo(LocalDate.of(2026, 7, 28));
+        assertThat(metadata.currency()).isEqualTo("EUR");
+        assertThat(metadata.iban()).isEqualTo("DE02120300000000202051");
+        assertThat(metadata.sender().name()).isEqualTo("Spedition Muster GmbH");
+        assertThat(metadata.sender().vatId()).isEqualTo("DE123456789");
+        assertThat(metadata.recipient().name()).isEqualTo("Kunde AG");
+        assertThat(metadata.recipient().zip()).isEqualTo("10115");
+        assertThat(metadata.recipient().email()).isEqualTo("rechnung@kunde-ag.de");
+        assertThat(metadata.items()).hasSize(2);
+        assertThat(metadata.items().get(0).description()).isEqualTo("Transport");
+        assertThat(metadata.items().get(0).quantity()).isEqualByComparingTo("12");
+        assertThat(metadata.items().get(0).unitPriceNet()).isEqualByComparingTo("5.00");
+        assertThat(metadata.items().get(0).vatPercent()).isEqualByComparingTo("19");
+    }
+
+    @Test
+    void signFallsBackToSingleLineForLegacyInvoiceWithoutItems() throws Exception {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        invoice.setItems(null);
+        invoice.setDescription("Kurierfahrt Hamburg–Berlin");
+        when(pdfToolService.signInvoice(any(), any()))
+                .thenReturn(new PdfToolService.SignedInvoice(new byte[] { 9 }, "re.zip", true));
+
+        service.sign(invoice);
+
+        verify(pdfToolService).signInvoice(any(), metadataCaptor.capture());
+        List<PdfToolService.LineItem> items = metadataCaptor.getValue().items();
+        assertThat(items).hasSize(1);
+        assertThat(items.get(0).description()).isEqualTo("Kurierfahrt Hamburg–Berlin");
+        assertThat(items.get(0).quantity()).isEqualByComparingTo("1");
+        assertThat(items.get(0).unitPriceNet()).isEqualByComparingTo("100.00");
+    }
+
+    @Test
+    void signUsesDefaultDatesWhenMissing() throws Exception {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        invoice.setDeliveryDate(null);
+        invoice.setPaymentDueDate(null);
+        when(pdfToolService.signInvoice(any(), any()))
+                .thenReturn(new PdfToolService.SignedInvoice(new byte[] { 9 }, "re.zip", true));
+
+        service.sign(invoice);
+
+        verify(pdfToolService).signInvoice(any(), metadataCaptor.capture());
+        PdfToolService.InvoiceMetadata metadata = metadataCaptor.getValue();
+        assertThat(metadata.deliveryDate()).isEqualTo(invoice.getInvoiceDate());
+        assertThat(metadata.dueDate()).isEqualTo(invoice.getInvoiceDate().plusDays(14));
+    }
+
+    @Test
+    void signRejectsInvoiceWithoutPdf() {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        invoice.setPdfData(null);
+
+        assertThatThrownBy(() -> service.sign(invoice)).isInstanceOf(IllegalStateException.class)
+                .hasMessageContaining("kein PDF");
+    }
+
+    @Test
+    void signRejectsInvoiceWithoutParties() {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        invoice.setSenderName(null);
+
+        assertThatThrownBy(() -> service.sign(invoice)).isInstanceOf(IllegalStateException.class)
+                .hasMessageContaining("Absender");
+    }
+
+    @Test
+    void signRejectsInvoiceWithoutAnyAmount() {
+        CustomerInvoice invoice = fullyPopulatedInvoice();
+        invoice.setItems(null);
+        invoice.setNetAmount(null);
+
+        assertThatThrownBy(() -> service.sign(invoice)).isInstanceOf(IllegalStateException.class)
+                .hasMessageContaining("Positionen");
+    }
+}