diff --git a/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml b/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml
index d0f8b2b..85bda12 100644
--- a/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml
+++ b/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml
@@ -16,10 +16,10 @@
 
 @if (!string.IsNullOrEmpty(Model.Invoice?.ResultFilePath))
 {
-    <button class="btn btn-primary mb-3 ms-2"
-            onclick="openPdfViewer(@Model.Invoice.Id)">
+    <a class="btn btn-primary mb-3 ms-2"
+       href="/Invoices/DocumentViewer?id=@Model.Invoice.Id">
         <i class="dx-icon-pdffile"></i> Ergebnis anzeigen
-    </button>
+    </a>
 }
 
 @if (Model.Invoice is null)
diff --git a/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml b/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml
new file mode 100644
index 0000000..2add8b7
--- /dev/null
+++ b/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml
@@ -0,0 +1,33 @@
+@page
+@model DXApp.TemplateKitProject.Pages.Invoices.DocumentViewerModel
+@{
+    ViewData["Title"] = "Dokument Viewer";
+    var pdfUrl = Model.PdfUrl;
+}
+
+<div class="container-fluid" style="height:100vh; padding:0;">
+    <div class="d-flex align-items-center justify-content-between p-3 border-bottom">
+        <h5 class="m-0">Rechnung @Model.Id - Dokument</h5>
+        <div>
+            <a class="btn btn-secondary me-2" href="/Invoices">Zurück zur Übersicht</a>
+            <!-- Später: Button um DevExpress Viewer zu öffnen -->
+            <a class="btn btn-outline-primary" href="/Invoices/DocumentViewerDevExpress?id=@Model.Id">
+                DevExpress Viewer (experimental)
+            </a>
+        </div>
+    </div>
+
+    <div style="height:calc(100vh - 64px);">
+        @* Solide, funktionierende Baseline: Browser-internen PDF-Renderer verwenden *@
+        <iframe id="pdf-viewer-iframe"
+                src="@pdfUrl"
+                style="width:100%; height:100%; border: none;"
+                title="PDF Viewer"></iframe>
+    </div>
+
+    @* Hinweis:
+       - Diese Seite zeigt aktuell das PDF per einfachem iframe (funktioniert zuverlässig).
+       - Nächster Commit: wir ersetzen iframe durch DevExpress WebDocumentViewer oder laden diesen zusätzlich.
+       - Der Link "DevExpress Viewer (experimental)" ist ein Platzhalter; wir implementieren die Route /Invoices/DocumentViewerDevExpress in einem der nächsten Schritte.
+    *@
+</div>
\ No newline at end of file
diff --git a/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml.cs b/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml.cs
new file mode 100644
index 0000000..021c7fc
--- /dev/null
+++ b/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml.cs
@@ -0,0 +1,17 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace DXApp.TemplateKitProject.Pages.Invoices;
+
+public class DocumentViewerModel : PageModel
+{
+    [BindProperty(SupportsGet = true)]
+    public int Id { get; set; }
+
+    public string PdfUrl => $"/Invoices/ViewPdf?id={Id}";
+
+    public void OnGet()
+    {
+        // Keine serverseitige Logik nötig für die erste Version.
+    }
+}
\ No newline at end of file
diff --git a/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs b/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs
index a13f182..83d5017 100644
--- a/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs
+++ b/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs
@@ -18,7 +18,6 @@ public class ViewPdfModel : PageModel
 
     public async Task<IActionResult> OnGetAsync(int id)
     {
-        // Sicherheit: defensive checks, gleiche Logik wie CustomReportStorageWebExtension
         var invoice = await _db.ZugferdInvoices
             .AsNoTracking()
             .FirstOrDefaultAsync(i => i.Id == id);
@@ -35,6 +34,10 @@ public class ViewPdfModel : PageModel
         var bytes = await System.IO.File.ReadAllBytesAsync(invoice.ResultFilePath);
         _logger.LogInformation("ViewPdf: Invoice {Id} ausgeliefert ({Size} Bytes).", id, bytes.Length);
 
-        return File(bytes, "application/pdf", $"{Path.GetFileName(invoice.ResultFilePath)}");
+        // Wichtig: keine "attachment" Content-Disposition setzen
+        // wir setzen inline (oder lassen es weg) damit Browser im Viewer darstellt
+        Response.Headers["Content-Disposition"] = $"inline; filename=\"{Path.GetFileName(invoice.ResultFilePath)}\"";
+
+        return File(bytes, "application/pdf");
     }
 }
\ No newline at end of file