diff --git a/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml b/DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml
index 85bda12..d0f8b2b 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))
 {
-    <a class="btn btn-primary mb-3 ms-2"
-       href="/Invoices/DocumentViewer?id=@Model.Invoice.Id">
+    <button class="btn btn-primary mb-3 ms-2"
+            onclick="openPdfViewer(@Model.Invoice.Id)">
         <i class="dx-icon-pdffile"></i> Ergebnis anzeigen
-    </a>
+    </button>
 }
 
 @if (Model.Invoice is null)
diff --git a/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml b/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml
deleted file mode 100644
index 2add8b7..0000000
--- a/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml
+++ /dev/null
@@ -1,33 +0,0 @@
-@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
deleted file mode 100644
index 021c7fc..0000000
--- a/DXApp.TemplateKitProject/Pages/Invoices/DocumentViewer.cshtml.cs
+++ /dev/null
@@ -1,17 +0,0 @@
-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 83d5017..a13f182 100644
--- a/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs
+++ b/DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs
@@ -18,6 +18,7 @@ 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);
@@ -34,10 +35,6 @@ public class ViewPdfModel : PageModel
         var bytes = await System.IO.File.ReadAllBytesAsync(invoice.ResultFilePath);
         _logger.LogInformation("ViewPdf: Invoice {Id} ausgeliefert ({Size} Bytes).", id, bytes.Length);
 
-        // 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");
+        return File(bytes, "application/pdf", $"{Path.GetFileName(invoice.ResultFilePath)}");
     }
 }
\ No newline at end of file