How to protect the attachments in existing PDF in WinForms?

The Syncfusion Essential® PDF is a feature rich and high-performance .NET PDF library used to create, read, and edit PDF documents programmatically without Adobe dependencies. This library also offers functionality to merge, split, stamp, forms, compress, and secure PDF files.

Using this library, you can encrypt only the attachment files in an existing PDF document using the EncryptOnlyAttachments encryption option.

Steps to protect the attachments in an existing PDF document programmatically in C#:

1. Create a new C# console application project.

2. Install the Syncfusion.Pdf.WinForms NuGet package as a reference to your .NET framework application from NuGet.org.
3. Include the following namespaces in the Program.cs file.

C#

using Syncfusion.Pdf;
using Syncfusion.Pdf.Interactive;
using Syncfusion.Pdf.Parsing; 
using Syncfusion.Pdf.Security;
using System.Drawing;

VB.NET

Imports Syncfusion.Pdf
Imports Syncfusion.Pdf.Interactive
Imports Syncfusion.Pdf.Parsing
Imports Syncfusion.Pdf.Security;
Imports System.Drawing

4. The Syncfusion® PDF Library supports encrypting only the attachment files in an existing PDF document using the EncryptOnlyAttachments option in PdfEncryptionOptions enum property.

C#

//Specifies encryption option
 
security.EncryptionOptions = PdfEncryptionOptions.EncryptOnlyAttachments;

       VB.NET

'Specifies encryption option
 
security.EncryptionOptions = PdfEncryptionOptions.EncryptOnlyAttachments
 

5. Include the following code snippet in the main method of Program.cs file to encrypt only the attachment files in an existing PDF document.

C#

//Load the PDF document
 
PdfLoadedDocument document = new PdfLoadedDocument(@"input.pdf");
 
//PDF document security
 
PdfSecurity security = document.Security;
 
//Specifies encryption key size, algorithm, and permission
 
security.KeySize = PdfEncryptionKeySize.Key256Bit;
 
security.Algorithm = PdfEncryptionAlgorithm.AES;
 
//Provide user password
 
security.UserPassword = "password";
 
//Specifies encryption option
 
security.EncryptionOptions = PdfEncryptionOptions.EncryptOnlyAttachments;
 
//Save the document
 
document.Save("Output.pdf");
 
//Close the document
 
document.Close(true);

VB.NET

'Load the PDF document
 
Dim document As New PdfLoadedDocument("Input.pdf")
 
'PDF document security
 
Dim security As PdfSecurity = document.Security
 
'Specifies encryption key size, algorithm, and permission
 
security.KeySize = PdfEncryptionKeySize.Key256Bit
 
security.Algorithm = PdfEncryptionAlgorithm.AES
 
'Provide user password
 
security.UserPassword = "password"
 
'Specifies encryption option
 
security.EncryptionOptions = PdfEncryptionOptions.EncryptOnlyAttachments
 
'Save the document
 
document.Save("Output.pdf")
 
'Close the document
 
document.Close(true)

 A complete working sample can be downloaded from AttachmentSample.Zip

 By executing the program, you will get the PDF document as follows.

Take a moment to peruse the documentation, where you will find other options like protect attachment in existing pdf document, protect an existing document, and encryption option .

Click here to explore the rich set of Syncfusion Essential® PDF features.

See Also:

Protect the pdf in .NET

Working with security

How to secure PDF file with passwords

Note:

Starting with v16.2.0.x, if you reference Syncfusion® assemblies from the trial setup or the NuGet feed, include a license key in your projects. Refer to the link to learn about generating and registering the Syncfusion® license key in your application to use the components without a trial message.

Conclusion:

I hope you enjoyed learning about how to protect the attachments in existing PDF in WinForms.

You can refer to our Flutter PDF feature tour page to learn about its other groundbreaking features and documentation, and how to quickly get started with configuration specifications. You can also explore our Flutter PDF Flutter PDF examples to understand how to create and manipulate data.

For current customers, you can check out our components from the License and Downloads page. If you are new to Syncfusion®, you can try our 30-day free trial to explore our other controls.

If you have any queries or require clarifications, please let us know in the comments section below. You can also contact us through our support forums or feedback portal. We are always happy to assist you!