How to Change PDF Password using C#. For more details: https://kb.aspose.com/pdf/net/how-to-change-pdf-password-using-csharp/

How to Change PDF Password using C#.cs

using System.Security.AccessControl;
using Aspose.Pdf;
using Aspose.Pdf.Facades;

namespace AsposeProjects
{
    class Program
    {
        static void Main(string[] args)
        {
            // Initialize license
            License lic = new License();
            lic.SetLicense("Aspose.Total.lic");

            // Instantiate the PdfFileInfo object
            PdfFileInfo fileInfo = new PdfFileInfo("PasswordPDF.pdf");

            // Check if the PDF file is encrypted using a password
            if (fileInfo.IsEncrypted == true)
            {
                // Instantiate a PdfFileSecurity object
                PdfFileSecurity security = new PdfFileSecurity();

                // Bind the PDF
                security.BindPdf("PasswordPDF.pdf");

                // Change the password
                security.ChangePassword("old_password", "new_user_password", "new_owner_password", DocumentPrivilege.Print, KeySize.x256);

                // Save the PDF
                security.Save("UpdatedPasswordPDF.pdf");
            }

            System.Console.WriteLine("Done");
        }
    }
}