This sample shows how to unprotect a document (if you know the password).

// Get a fresh copy of the sample PDF file.
// The passwords are 'user' and 'owner' in this sample.
string filename = "HelloWorld (protected).pdf";
File.Copy(Path.Combine("../../../../PDFs/", filename), 
  Path.Combine(Directory.GetCurrentDirectory(), filename), true);
 
PdfDocument document;
 
// Opening a document will fail with an invalid password.
try
{
  document = PdfReader.Open(filename, "invalid password");
}
catch (Exception ex)
{
  Debug.WriteLine(ex.Message);
}
 
// You can specifiy a delegate, which is called if the document needs a
// password. If you want to modify the document, you must provide the
// owner password.
document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify,
  new PdfPasswordProvider(PasswordProvider));
 
// Open the document with the user password.
document = PdfReader.Open(filename, "user", PdfDocumentOpenMode.ReadOnly);
 
// Use the property HasOwnerPermissions to decide whether the used password
// was the user or the owner password. In both cases PDFsharp provides full
// access to the PDF document. It is up to the programmer who uses PDFsharp
// to honor the access rights. PDFsharp doesn't try to protect the document
// because this make little sence for an open source library.
bool hasOwnerAccess = document.SecuritySettings.HasOwnerPermissions;
 
// Open the document with the owenr password.
document = PdfReader.Open(filename, "owner");
hasOwnerAccess = document.SecuritySettings.HasOwnerPermissions;
 
// A document opened with the owner password is completely unprotected
// and can be modified.
XGraphics gfx = XGraphics.FromPdfPage(document.Pages[0]);
gfx.DrawString("Some text...",
  new XFont("Times", 12), XBrushes.Firebrick, 50, 100);
 
// The modified document is saved without any protection applied.
PdfDocumentSecurityLevel level = document.SecuritySettings.DocumentSecurityLevel;
 
// If you want to save it protected, you must set the DocumentSecurityLevel
// or apply new passwords.
// In the current implementation the old passwords are not automatically
// reused. See 'ProtectDocument' sample for further information.
 
// Save the document...
document.Save(filename);
// ...and start a viewer.
Process.Start(filename);