Revert "Enhance PDF viewing experience with new document viewer"

This reverts commit 1cc617de42.

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)}");
     }
 }