diff --git a/backend/src/controllers/fileDownload.controller.ts b/backend/src/controllers/fileDownload.controller.ts
index c5f31975..fed0e70c 100644
--- a/backend/src/controllers/fileDownload.controller.ts
+++ b/backend/src/controllers/fileDownload.controller.ts
@@ -84,15 +84,51 @@ export async function downloadFile(req: AuthRequest, res: Response): Promise<voi
   // durch und wurde mit Original-Extension auf Disk geschrieben.
   // Beim Download bestimmt res.sendFile() den Content-Type aus der
   // Extension – also `text/html` – und der Browser hätte das als
-  // Stored-XSS gerendert. `X-Content-Type-Options: nosniff` schützt
-  // nicht, wenn der Server selbst text/html liefert.
+  // Stored-XSS gerendert.
   //
-  // Fix: alle Files via Content-Disposition: attachment ausliefern.
-  // Der Browser lädt herunter statt zu rendern, egal welcher Type.
-  // Für legitime PDF/Bild-Vorschau ist das vertretbar – Browser
-  // öffnen den Download dann eben aus dem Datei-Manager.
+  // Default: Content-Disposition: attachment → Browser lädt nur runter.
+  // Opt-in inline-Vorschau (Bank-Karten/Ausweis-Anzeigen-Button) per
+  // ?disposition=inline, ABER nur wenn die ersten Bytes der Datei das
+  // Magic eines bekannten safe Typs (PDF, PNG, JPEG, GIF, WebP) zeigen.
+  // Bei Mismatch fällt's auf attachment zurück – Stored XSS bleibt
+  // weiterhin unmöglich.
   const filename = path.basename(absolute).replace(/[^A-Za-z0-9._-]/g, '_');
+  const wantsInline = req.query.disposition === 'inline';
+  let useInline = false;
+  let inlineContentType: string | null = null;
+  if (wantsInline) {
+    try {
+      const fd = fs.openSync(absolute, 'r');
+      const head = Buffer.alloc(12);
+      fs.readSync(fd, head, 0, 12, 0);
+      fs.closeSync(fd);
+      if (head.subarray(0, 5).toString('latin1') === '%PDF-') {
+        useInline = true;
+        inlineContentType = 'application/pdf';
+      } else if (head.subarray(0, 8).equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]))) {
+        useInline = true;
+        inlineContentType = 'image/png';
+      } else if (head[0] === 0xff && head[1] === 0xd8 && head[2] === 0xff) {
+        useInline = true;
+        inlineContentType = 'image/jpeg';
+      } else if (head.subarray(0, 6).toString('latin1') === 'GIF87a'
+              || head.subarray(0, 6).toString('latin1') === 'GIF89a') {
+        useInline = true;
+        inlineContentType = 'image/gif';
+      } else if (head.subarray(0, 4).toString('latin1') === 'RIFF'
+              && head.subarray(8, 12).toString('latin1') === 'WEBP') {
+        useInline = true;
+        inlineContentType = 'image/webp';
+      }
+    } catch { /* ignore – fällt auf attachment zurück */ }
+  }
+
   res.setHeader('X-Content-Type-Options', 'nosniff');
-  res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
+  if (useInline && inlineContentType) {
+    res.setHeader('Content-Type', inlineContentType);
+    res.setHeader('Content-Disposition', `inline; filename="${filename}"`);
+  } else {
+    res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
+  }
   res.sendFile(absolute);
 }
diff --git a/frontend/src/components/contracts/InvoicesSection.tsx b/frontend/src/components/contracts/InvoicesSection.tsx
index 9b0669ce..2cdd5a47 100644
--- a/frontend/src/components/contracts/InvoicesSection.tsx
+++ b/frontend/src/components/contracts/InvoicesSection.tsx
@@ -9,7 +9,7 @@ import Select from '../ui/Select';
 import Badge from '../ui/Badge';
 import { invoiceApi } from '../../services/api';
 import type { Invoice, InvoiceType } from '../../types';
-import { fileUrl } from '../../utils/fileUrl';
+import { fileUrl, viewUrl } from '../../utils/fileUrl';
 
 const invoiceTypeLabels: Record<InvoiceType, string> = {
   INTERIM: 'Zwischenrechnung',
@@ -121,7 +121,7 @@ export default function InvoicesSection({
                 {invoice.documentPath && (
                   <div className="flex items-center gap-2">
                     <a
-                      href={fileUrl(invoice.documentPath)}
+                      href={viewUrl(invoice.documentPath)}
                       target="_blank"
                       rel="noopener noreferrer"
                       className="flex items-center gap-1 text-blue-600 hover:text-blue-800 text-sm"
diff --git a/frontend/src/pages/contracts/ContractDetail.tsx b/frontend/src/pages/contracts/ContractDetail.tsx
index b23ff303..f728945c 100644
--- a/frontend/src/pages/contracts/ContractDetail.tsx
+++ b/frontend/src/pages/contracts/ContractDetail.tsx
@@ -20,7 +20,7 @@ import CopyButton, { CopyableBlock } from '../../components/ui/CopyButton';
 import { formatDate } from '../../utils/dateFormat';
 import { useProviderSettings } from '../../hooks/useProviderSettings';
 import type { ContractType, ContractStatus, SimCard, MeterReading, ContractTask, ContractTaskSubtask, ContractMeter, ContractDocument } from '../../types';
-import { fileUrl } from '../../utils/fileUrl';
+import { fileUrl, viewUrl } from '../../utils/fileUrl';
 
 const typeLabels: Record<ContractType, string> = {
   ELECTRICITY: 'Strom',
@@ -2118,7 +2118,7 @@ export default function ContractDetail() {
                   {c.cancellationLetterPath ? (
                     <div className="flex items-center gap-3 flex-wrap">
                       <a
-                        href={fileUrl(c.cancellationLetterPath)}
+                        href={viewUrl(c.cancellationLetterPath)}
                         target="_blank"
                         rel="noopener noreferrer"
                         className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -2175,7 +2175,7 @@ export default function ContractDetail() {
                     <>
                       <div className="flex items-center gap-3 flex-wrap">
                         <a
-                          href={fileUrl(c.cancellationConfirmationPath)}
+                          href={viewUrl(c.cancellationConfirmationPath)}
                           target="_blank"
                           rel="noopener noreferrer"
                           className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -2261,7 +2261,7 @@ export default function ContractDetail() {
                   {c.cancellationLetterOptionsPath ? (
                     <div className="flex items-center gap-3 flex-wrap">
                       <a
-                        href={fileUrl(c.cancellationLetterOptionsPath)}
+                        href={viewUrl(c.cancellationLetterOptionsPath)}
                         target="_blank"
                         rel="noopener noreferrer"
                         className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -2318,7 +2318,7 @@ export default function ContractDetail() {
                     <>
                       <div className="flex items-center gap-3 flex-wrap">
                         <a
-                          href={fileUrl(c.cancellationConfirmationOptionsPath)}
+                          href={viewUrl(c.cancellationConfirmationOptionsPath)}
                           target="_blank"
                           rel="noopener noreferrer"
                           className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -3484,7 +3484,7 @@ function ContractDocumentsSection({
                       {doc.documentType}
                     </span>
                     <a
-                      href={fileUrl(doc.documentPath)}
+                      href={viewUrl(doc.documentPath)}
                       target="_blank"
                       rel="noopener noreferrer"
                       className="text-sm text-blue-600 hover:underline"
diff --git a/frontend/src/pages/customers/CustomerDetail.tsx b/frontend/src/pages/customers/CustomerDetail.tsx
index 4f2824f4..2012e43d 100644
--- a/frontend/src/pages/customers/CustomerDetail.tsx
+++ b/frontend/src/pages/customers/CustomerDetail.tsx
@@ -21,7 +21,7 @@ import { formatDate } from '../../utils/dateFormat';
 import { getContractTypeInfo } from '../../utils/contractInfo';
 import { useProviderSettings } from '../../hooks/useProviderSettings';
 import type { Address, BankCard, IdentityDocument, Meter, Customer, CustomerRepresentative, CustomerSummary, CustomerConsent, ConsentType, ConsentStatus, RepresentativeAuthorization } from '../../types';
-import { fileUrl } from '../../utils/fileUrl';
+import { fileUrl, viewUrl } from '../../utils/fileUrl';
 
 export default function CustomerDetail({ portalCustomerId }: { portalCustomerId?: number } = {}) {
   const { id } = useParams();
@@ -577,7 +577,7 @@ function BusinessDataCard({
           {customer.businessRegistrationPath ? (
             <div className="flex items-center gap-2 flex-wrap">
               <a
-                href={fileUrl(customer.businessRegistrationPath)}
+                href={viewUrl(customer.businessRegistrationPath)}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -628,7 +628,7 @@ function BusinessDataCard({
           {customer.commercialRegisterPath ? (
             <div className="flex items-center gap-2 flex-wrap">
               <a
-                href={fileUrl(customer.commercialRegisterPath)}
+                href={viewUrl(customer.commercialRegisterPath)}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -948,7 +948,7 @@ function BankCardsTab({
                 {card.documentPath ? (
                   <div className="flex items-center gap-2 flex-wrap">
                     <a
-                      href={fileUrl(card.documentPath)}
+                      href={viewUrl(card.documentPath)}
                       target="_blank"
                       rel="noopener noreferrer"
                       className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -1184,7 +1184,7 @@ function DocumentsTab({
                 {doc.documentPath ? (
                   <div className="flex items-center gap-2 flex-wrap">
                     <a
-                      href={fileUrl(doc.documentPath)}
+                      href={viewUrl(doc.documentPath)}
                       target="_blank"
                       rel="noopener noreferrer"
                       className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -4123,7 +4123,7 @@ function ConsentTab({
           {customer.privacyPolicyPath ? (
             <div className="flex items-center gap-3 flex-wrap">
               <a
-                href={fileUrl(customer.privacyPolicyPath)}
+                href={viewUrl(customer.privacyPolicyPath)}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="text-blue-600 hover:underline text-sm flex items-center gap-1"
@@ -4441,7 +4441,7 @@ function AuthorizationsSection({ customerId, customerEmail }: { customerId: numb
               {auth.documentPath ? (
                 <>
                   <a
-                    href={fileUrl(auth.documentPath)}
+                    href={viewUrl(auth.documentPath)}
                     target="_blank"
                     rel="noopener noreferrer"
                     className="text-blue-600 hover:underline text-xs flex items-center gap-1"
diff --git a/frontend/src/pages/settings/GDPRDashboard.tsx b/frontend/src/pages/settings/GDPRDashboard.tsx
index b65f5983..79970570 100644
--- a/frontend/src/pages/settings/GDPRDashboard.tsx
+++ b/frontend/src/pages/settings/GDPRDashboard.tsx
@@ -7,7 +7,7 @@ import Card from '../../components/ui/Card';
 import Button from '../../components/ui/Button';
 import Select from '../../components/ui/Select';
 import { ArrowLeft, FileText, Users, CheckCircle, Clock, XCircle, AlertTriangle, Download, X, ChevronRight } from 'lucide-react';
-import { fileUrl } from '../../utils/fileUrl';
+import { viewUrl } from '../../utils/fileUrl';
 import { useAuth } from '../../context/AuthContext';
 
 const STATUS_OPTIONS = [
@@ -364,7 +364,7 @@ export default function GDPRDashboard() {
                         <Button
                           variant="ghost"
                           size="sm"
-                          onClick={() => window.open(fileUrl(`/uploads/${request.proofDocument}`), '_blank')}
+                          onClick={() => window.open(viewUrl(`/uploads/${request.proofDocument}`), '_blank')}
                           title="Löschnachweis anzeigen"
                         >
                           <FileText className="w-4 h-4 text-blue-500" />
diff --git a/frontend/src/pages/settings/PdfTemplates.tsx b/frontend/src/pages/settings/PdfTemplates.tsx
index b3341db4..5d785a32 100644
--- a/frontend/src/pages/settings/PdfTemplates.tsx
+++ b/frontend/src/pages/settings/PdfTemplates.tsx
@@ -9,7 +9,7 @@ import Input from '../../components/ui/Input';
 import Badge from '../../components/ui/Badge';
 import Modal from '../../components/ui/Modal';
 import { ArrowLeft, Plus, Edit, Trash2, FileText, Upload, Link2, Eye, Play } from 'lucide-react';
-import { fileUrl } from '../../utils/fileUrl';
+import { viewUrl } from '../../utils/fileUrl';
 
 export default function PdfTemplates() {
   const navigate = useNavigate();
@@ -96,7 +96,7 @@ export default function PdfTemplates() {
                   <Button variant="ghost" size="sm" onClick={() => setTestTemplate(t)} title="Testvorschau mit Vertragsdaten">
                     <Play className="w-4 h-4 text-green-500" />
                   </Button>
-                  <a href={fileUrl(t.templatePath)} target="_blank" rel="noopener noreferrer">
+                  <a href={viewUrl(t.templatePath)} target="_blank" rel="noopener noreferrer">
                     <Button variant="ghost" size="sm" title="Leere Vorlage anzeigen">
                       <Eye className="w-4 h-4" />
                     </Button>
diff --git a/frontend/src/utils/fileUrl.ts b/frontend/src/utils/fileUrl.ts
index 742735ac..c205f1d2 100644
--- a/frontend/src/utils/fileUrl.ts
+++ b/frontend/src/utils/fileUrl.ts
@@ -15,11 +15,25 @@
  */
 import { getAccessToken } from '../services/api';
 
-export function fileUrl(path: string | null | undefined): string {
+/**
+ * Kurzform für Inline-Vorschau: identisch zu `fileUrl(path, { inline: true })`.
+ * Verwenden für „Anzeigen"-Links / target="_blank"-Vorschauen. Default-
+ * `fileUrl(path)` bleibt für Downloads (Content-Disposition: attachment).
+ */
+export function viewUrl(path: string | null | undefined): string {
+  return fileUrl(path, { inline: true });
+}
+
+export function fileUrl(path: string | null | undefined, opts?: { inline?: boolean }): string {
   if (!path) return '';
   const token = getAccessToken();
   const normalizedPath = path.startsWith('/') ? path : '/' + path;
-  const base = `/api/files/download?path=${encodeURIComponent(normalizedPath)}`;
+  // `?disposition=inline` schaltet die Anzeige im Browser-Tab ein,
+  // der Backend-Controller bleibt aber nur dann inline, wenn die
+  // Datei tatsächlich ein safe Type (PDF/PNG/JPEG/GIF/WebP) ist –
+  // sonst fällt's auf attachment zurück. Default attachment.
+  const dispParam = opts?.inline ? '&disposition=inline' : '';
+  const base = `/api/files/download?path=${encodeURIComponent(normalizedPath)}${dispParam}`;
   if (!token) return base;
   return `${base}&token=${encodeURIComponent(token)}`;
 }