How to secure PDF file with passwords in Flutter PDF?

 Our Flutter PDF feature tour page is used to create, read, and edit PDF documents. Using this library, you can protect the PDF document using encryption and set permission to the PDF document operations like printing, editing, copy content, and more. The Flutter PDF library supports the basic to advanced encryption standards.

• RC4 40-bit
• RC4 128-bit
• AES 128-bit
• AES 256-bit Revision 5
• AES 256-bit Revision 6 (PDF 2.0)

Steps to protect PDF document programmatically:

1. Create a new Flutter application project.

1.1.Open Visual Studio Code (After installing the Dart and Flutter extensions as stated in the setup editor page).

1.2.Click View -> Command Palette…

1.3.Type Flutter and choose Flutter: New Application Project.

1.4.Enter the project name and press the Enter button.

1.5.Now, choose the location of the project.

2. Add the following code in your pubspec.yaml file to install the syncfusion flutter pdf package in your application. It will be automatically downloaded from the pub once you trigger the flutter pub get comment or Get packages option from the Visual Studio Code.

   dependencies:
     syncfusion_flutter_pdf: ^20.3.49
   

3. Import the following syncfusion_flutter_pdf package in your main.dart file.

   import 'package:syncfusion_flutter_pdf/pdf.dart';
   

4. Add the following code in the lib/main.dart file to create a simple button.

   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
         title: Text(widget.title),
       ),
       body: Center(
         child: Column(
           mainAxisAlignment: MainAxisAlignment.center,
           children: <Widget>[
             TextButton(
               child: Text(
                 'Secure PDF',
                 style: TextStyle(color: Colors.white),
               ),
               style: ButtonStyle(
                   backgroundColor: MaterialStateProperty.resolveWith(
                       (states) => Colors.blue)),
               onPressed: securePdf,
             )
           ],
         ),
       ),
     );
   }
   

5. Add the following code to the securePdf function to secure PDF documents programmatically.

   Future<void> securePdf() async {
     //Load the existing PDF document.
     PdfDocument document = PdfDocument(
         inputBytes: await _readDocumentData('credit_card_statement.pdf'));
     //Get the document security and set user and owner password.
     document.security.userPassword = 'password@123';
     document.security.ownerPassword = 'owner@123';
     //Set the encryption algorithm and permissions.
     document.security.algorithm = PdfEncryptionAlgorithm.aesx256Bit;
     document.security.permissions
         .addAll([PdfPermissionsFlags.print, PdfPermissionsFlags.copyContent]);
     //Save and dispose the document.
     List<int> bytes = await document.save();
     document.dispose();
     //Save the file and launch/download.
     SaveFile.saveAndLaunchFile(bytes, 'output.pdf');
   }
   

6. Include the following code to read the PDF document from the folder where it is saved. Here, we have named our folder called assets.

   Future<List<int>> _readDocumentData(String name) async {
     final ByteData data = await rootBundle.load('assets/$name');
     return data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
   }
   

7. Before that, mention the input document in the assets section of the pubspec.yaml file as stated below.

   # To add assets to your application, add an assets section, like this:
   assets:
     - assets/credit_card_statement.pdf
   

8. Follow the steps to save and launch the generated PDF file.

Web:

8.1. Add the web package as a dependency in your pubspec.yaml file. Then, create a new Dart file named save_file_web.dart. Finally, add the following code to implement the file download functionality using the web package.

import 'dart:convert';
import 'package:web/web.dart' as web;

8.2.To enable file saving and initiate downloads in a Flutter web environment, use the following code within the saveAndLaunchFile method.

// Function to save and launch a file for download in a web environment
Future<void> saveAndLaunchFile(List<int> bytes, String fileName) async {
  final web.HTMLAnchorElement anchor =
      web.document.createElement('a') as web.HTMLAnchorElement
        ..href = "data:application/octet-stream;base64,${base64Encode(bytes)}"
        ..style.display = 'none'
        ..download = fileName;

// Insert the new element into the DOM
web.document.body!.appendChild(anchor);

// Initiate the download
anchor.click();
// Clean up the DOM by removing the anchor element
web.document.body!.removeChild(anchor);
}

       Desktop and Mobile:

8.3.Add the following dependencies in your pubspec.yaml file.

open_file: ^3.2.1   #Open source library to launch the PDF file in mobile devices
path_provider: ^2.0.11

8.4.Create a new dart file named save_file_mobile_and_desktop.dart under the lib folder and import the following packages in save_file_mobile_and_desktop.dart file.

import 'dart:io';
import 'package:open_file/open_file.dart';
import 'package:path_provider/path_provider.dart';

8.5.Include the following code snippet in save_file_mobile_and_desktop.dart to open the PDF document in Desktop and Mobile.

 class SaveFile {
  static Future<void> saveAndLaunchFile(
      List<int> bytes, String fileName) async {
    //Get external storage directory
    Directory directory = await getApplicationSupportDirectory();
    //Get directory path
    String path = directory.path;
    //Create an empty file to write PDF data
    File file = File('$path/$fileName');
    //Write PDF data
    await file.writeAsBytes(bytes, flush: true);
    //Open the PDF document in mobile
    OpenFile.open('$path/$fileName');
  }
}

9. Run the sample using the flutter run command. This will create an encrypted PDF document. After the application launches, you will get the PDF document as follows.

A complete working sample can be downloaded from secure_pdf.zip

Take a moment to peruse the documentation. You can find other options like AES Encryption, protect an existing document, changing the password, remove the password, changing the permission of PDF documents,  and features like adding layers, interactive annotations, and insert a hyperlink to PDF with code examples.