added file saver

lib/utils/FileSaver.dart

@@ -0,0 +1,23 @@
+import 'dart:io';
+
+import 'package:permission_handler/permission_handler.dart';
+
+// only tested on android!
+class FileSaver {
+  static Future<String> getExternalDocumentPath() async {
+    var permission = await Permission.storage.status;
+    if(!permission.isGranted) {
+      await Permission.storage.request();
+    }
+    var directory = Directory('/storage/emulated/0/Download');
+    final externalPath = directory.path;
+    await Directory(externalPath).create(recursive: true);
+    return externalPath;
+  }
+
+  static Future<File> writeBytes(List<int> bytes, String name) async {
+    final path = await getExternalDocumentPath();
+    var file = File('$path/$name');
+    return file.writeAsBytes(bytes);
+  }
+}

lib/widget/fileViewer.dart

@@ -9,6 +9,8 @@ import 'package:share_plus/share_plus.dart';
 import 'package:syncfusion_flutter_pdfviewer/pdfviewer.dart';
 
 import '../storage/base/settingsProvider.dart';
+import '../utils/FileSaver.dart';
+import 'infoDialog.dart';
 import 'placeholderView.dart';
 import 'sharePositionOrigin.dart';
 
@@ -53,6 +55,17 @@ class _FileViewerState extends State<FileViewer> {
             },
             icon: const Icon(Icons.share_outlined),
           ),
+          Visibility(
+            visible: Platform.isAndroid,
+            child: IconButton(
+              onPressed: () async {
+                await FileSaver.writeBytes(await File(widget.path).readAsBytes(), widget.path.split('/').last);
+                if(!context.mounted) return;
+                InfoDialog.show(context, 'Die Datei wurde im Downloads Ordner gespeichert.');
+              },
+              icon: const Icon(Icons.save_alt_outlined)
+            )
+          ),
           ...actions
         ],
       );