C#/VB.NET: Encrypt or Decrypt PDF Files

PDF encryption is a crucial task when it comes to sharing confidential documents on the Internet. By encrypting PDF files with strong passwords, you can protect the file data from being accessed by unauthorized parties. In certain cases, it may also be necessary to remove the password to make the document public. In this article, you will learn how to programmatically encrypt or decrypt a PDF file using Spire.PDF for .NET.

• Encrypt a PDF File with Password
• Remove Password to Decrypt a PDF File

Install Spire.PDF for .NET

To begin with, you need to add the DLL files included in the Spire.PDF for.NET package as references in your .NET project. The DLLs files can be either downloaded from this link or installed via NuGet.

PM> Install-Package Spire.PDF

Encrypt a PDF File with Password

There are two kinds of passwords for encrypting a PDF file - open password and permission password. The former is set to open the PDF file, while the latter is set to restrict printing, contents copying, commenting, etc. If a PDF file is secured with both types of passwords, it can be opened with either password.

The PdfSecurity.Encrypt(string openPassword, string permissionPassword, PdfPermissionsFlags permissions, PdfEncryptionKeySize keySize) method offered by Spire.PDF for .NET allows you to set both open password and permission password to encrypt PDF files. The detailed steps are as follows.

• Create a PdfDocument object.
• Load a sample PDF file using PdfDocument.LoadFromFile() method.
• Gets the security parameters of the document using PdfDocument.Security property.
• Encrypt the PDF file with open password and permission password using PdfSecurity.Encrypt(string openPassword, string permissionPassword, PdfPermissionsFlags permissions, PdfEncryptionKeySize keySize) method.
• Save the result file using PdfDocument.SaveToFile() method.

using Spire.Pdf;
using Spire.Pdf.Security;

namespace EncryptPDF
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load a sample PDF file
            pdf.LoadFromFile(@"E:\Files\sample.pdf");

            //Encrypt the PDF file with password
            pdf.Security.Encrypt("open", "permission", PdfPermissionsFlags.Print | PdfPermissionsFlags.CopyContent, PdfEncryptionKeySize.Key128Bit);

            //Save the result file
            pdf.SaveToFile("Encrypt.pdf", FileFormat.PDF);
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Security

Namespace EncryptPDF
    Class Program
        Private Shared Sub Main(ByVal args As String())

            'Create a PdfDocument object
            Dim pdf As PdfDocument = New PdfDocument()

            'Load a sample PDF file
            pdf.LoadFromFile("E:\Files\sample.pdf")

            'Encrypt the PDF file with password
            pdf.Security.Encrypt("open", "permission", PdfPermissionsFlags.Print Or PdfPermissionsFlags.CopyContent, PdfEncryptionKeySize.Key128Bit)

            'Save the result file
            pdf.SaveToFile("Encrypt.pdf", FileFormat.PDF)
        End Sub
    End Class
End Namespace

Remove Password to Decrypt a PDF File

When you need to remove the password from a PDF file, you can set the open password and permission password to empty while calling the PdfSecurity.Encrypt(string openPassword, string permissionPassword, PdfPermissionsFlags permissions, PdfEncryptionKeySize keySize, string originalPermissionPassword) method. The detailed steps are as follows.

• Create a PdfDocument object.
• Load the encrypted PDF file with password using PdfDocument.LoadFromFile (string filename, string password) method.
• Gets the security parameters of the document using PdfDocument.Security property.
• Decrypt the PDF file by setting the open password and permission password to empty using PdfSecurity.Encrypt(string openPassword, string permissionPassword, PdfPermissionsFlags permissions, PdfEncryptionKeySize keySize, string originalPermissionPassword) method.
• Save the result file using PdfDocument.SaveToFile() method.

using Spire.Pdf;
using Spire.Pdf.Security;

namespace DecryptPDF
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a PdfDocument object
            PdfDocument pdf = new PdfDocument();

            //Load the encrypted PDF file with password
            pdf.LoadFromFile("Encrypt.pdf", "open");

            //Set the password as empty to decrypt PDF
            pdf.Security.Encrypt(string.Empty, string.Empty, PdfPermissionsFlags.Default, PdfEncryptionKeySize.Key128Bit, "permission");

            //Save the result file
            pdf.SaveToFile("Decrypt.pdf", FileFormat.PDF);
        }
    }
} 

Imports Spire.Pdf
Imports Spire.Pdf.Security

Namespace DecryptPDF
    Class Program
        Private Shared Sub Main(ByVal args As String())

            'Create a PdfDocument object
            Dim pdf As PdfDocument = New PdfDocument()

            'Load the encrypted PDF file with password
            pdf.LoadFromFile("Encrypt.pdf", "open")

            'Set the password as empty to decrypt PDF
            pdf.Security.Encrypt(String.Empty, String.Empty, PdfPermissionsFlags.[Default], PdfEncryptionKeySize.Key128Bit, "permission")

            'Save the result file
            pdf.SaveToFile("Decrypt.pdf", FileFormat.PDF)
        End Sub
    End Class
End Namespace

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