diff --git a/src/Controllers/InvoiceController.php b/src/Controllers/InvoiceController.php
index 7a3f4c8..1eaeec4 100644
--- a/src/Controllers/InvoiceController.php
+++ b/src/Controllers/InvoiceController.php
@@ -275,12 +275,13 @@ class InvoiceController
         if (!$invoice) { http_response_code(404); return; }
 
         // Gespeicherte PDF aus dem Beleg ausliefern (GoBD: unveränderlicher Stand)
+        $beleg = null;
         if (!empty($invoice['beleg_id'])) {
             $beleg   = Beleg::find((int)$invoice['beleg_id']);
             $absPath = $beleg
                 ? dirname(__DIR__, 2) . '/public/' . $beleg['storage_path']
                 : '';
-            if ($absPath && file_exists($absPath)) {
+            if ($absPath && is_file($absPath)) {
                 header('Content-Type: application/pdf');
                 header('Content-Disposition: attachment; filename="' . $beleg['filename'] . '"');
                 header('Content-Length: ' . filesize($absPath));
@@ -289,7 +290,7 @@ class InvoiceController
             }
         }
 
-        // Fallback: PDF on-the-fly generieren (Entwurf oder Beleg noch ohne Datei)
+        // PDF generieren (Entwurf oder Altrechnung ohne gespeicherte Datei)
         if (!empty($invoice['storno_of_id'])) {
             $original = Invoice::find((int)$invoice['storno_of_id']);
             if ($original) {
@@ -302,7 +303,37 @@ class InvoiceController
         $settings = Setting::get();
 
         $svc = new PdfInvoiceService();
-        $svc->render($invoice, $lines, $settings);
+        $pdf = $svc->renderToString($invoice, $lines, $settings);
+
+        // Finalisierte Altrechnung: PDF nachträglich im Beleg speichern
+        if ($invoice['status'] !== 'Entwurf' && $beleg !== null) {
+            if (!empty($beleg['storage_path'])) {
+                $relPath = $beleg['storage_path'];
+                $absDir  = dirname(dirname(__DIR__, 2) . '/public/' . $relPath);
+            } else {
+                $year    = date('Y', strtotime($invoice['rechnungs_datum']));
+                $relDir  = 'static/uploads/' . $year . '/' . $beleg['beleg_nr'];
+                $relPath = $relDir . '/original.pdf';
+                $absDir  = dirname(__DIR__, 2) . '/public/' . $relDir;
+            }
+            if (!is_dir($absDir)) {
+                mkdir($absDir, 0755, true);
+            }
+            $absFilePath = dirname(__DIR__, 2) . '/public/' . $relPath;
+            file_put_contents($absFilePath, $pdf);
+            \Steuerkram\Database::execute(
+                'UPDATE belege SET storage_path=?, filename=?, file_hash=?, updated_at=NOW() WHERE id=?',
+                [$relPath, ($invoice['rechnungs_nr'] ?? 'Rechnung') . '.pdf', hash('sha256', $pdf), (int)$invoice['beleg_id']]
+            );
+        }
+
+        $prefix   = !empty($invoice['storno_of_id']) ? 'Stornorechnung-' : 'Rechnung-';
+        $filename = $prefix . ($invoice['rechnungs_nr'] ?? 'Entwurf') . '.pdf';
+
+        header('Content-Type: application/pdf');
+        header('Content-Disposition: attachment; filename="' . $filename . '"');
+        header('Content-Length: ' . strlen($pdf));
+        echo $pdf;
     }
 
     public function book(array $params): void
diff --git a/src/version.txt b/src/version.txt
index af7d1fa..5814d3d 100644
--- a/src/version.txt
+++ b/src/version.txt
@@ -1 +1 @@
-1-260505
+1-260506