Protect PDFs in C# with the .NET PDF Library

Step 1: Create a new C# Console Application project

Begin by creating a new C# Console Application project in Visual Studio or your preferred IDE to implement PDF security functionality.

Step 2: Install Syncfusion PDF NuGet package

Install the Syncfusion.Pdf.Net.Core NuGet package in your C# project from NuGet.org. This package provides PDF encryption and security APIs.

Step 3: Add required namespaces for PDF protection

Import the following namespaces in your Program.cs file to access PDF security classes and encryption methods:

using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;

Step 4: Load the PDF document to protect

Use the PdfLoadedDocument class to load your existing PDF file that you want to encrypt and password protect.

//Load the PDF document
using (PdfLoadedDocument loadedDocument = new PdfLoadedDocument(Path.GetFullPath(@"Data/Input.pdf")))
{
}

Step 5: Configure PDF security

Get the PdfSecurity object from the loaded document. Set the encryption algorithm to AES (Advanced Encryption Standard) and specify a 256-bit key size for maximum security protection.

Run

// Get the security settings of the document
PdfSecurity security = loadedDocument.Security;
// Set encryption to AES with a 256-bit key
security.KeySize = PdfEncryptionKeySize.Key256Bit;
security.Algorithm = PdfEncryptionAlgorithm.AES;

Step 6: Set owner and user passwords

Configure both owner and user passwords. The owner password allows full access to modify security settings, while the user password restricts document access.

// Set owner and user passwords for the document
security.OwnerPassword = "owner123";
security.UserPassword = "user123";

Step 7: Save the password-protected PDF document

Save the encrypted PDF document using the Save method. The output file will be protected with AES encryption and require passwords to access.

// Save the secured PDF document
loadedDocument.Save(Path.GetFullPath(@"Output/Output.pdf"));