Open PDFSharp Document and Saving Removes Password

Question

I am using PDFSharp in 2 different applications for 2 different reasons. The first is password protect a document and the second is to watermark the document. These processes both work individually in there own applications/workflows. The problem is that application 1 only knows about the password and application 2 only knows about the watermark, application 1 uses a default owner password and a dynamic user password, application 2 opens the document with the owner password to apply the watermark. The problem is that the password is not persisted, it seems PDFSharp while saving the document ignores the previous PDF password?!

Is there a way of keeping the security settings when applying the watermark, without explicitly defining the passwords again?

I posted this on the PDFSharp forum but they are ignoring it which is not a good sign?! http://forum.pdfsharp.net/viewtopic.php?f=2&t=2003&p=5737#p5737

Kind Regards,

Answer 1

I think this was a limitation of PDF sharp, as I got no response or help from them on there forum. I opened up there code and made the following changes to correct the error. Firstly i added a new property on the SecurityHandler.cs class

public string OwnerPassword
{
  set { SecurityHandler.OwnerPassword = value; }
}

/// <summary>
/// TODO: JOSH
/// </summary>
public bool MaintainOwnerAndUserPassword
{
    get { return SecurityHandler.MaintainOwnerAndUserPassword; }
    set { SecurityHandler.MaintainOwnerAndUserPassword = value; }
}

Then I changed the doSave method on the PdfDocument.cs class to look like the following:

    void DoSave(PdfWriter writer)
{
  if (this.pages == null || this.pages.Count == 0)
    throw new InvalidOperationException("Cannot save a PDF document with no pages.");

  try
  {
    bool encrypt = this.securitySettings.DocumentSecurityLevel != PdfDocumentSecurityLevel.None;
    if (encrypt)
    {
      PdfStandardSecurityHandler securityHandler = this.securitySettings.SecurityHandler;
      if (securityHandler.Reference == null)
        this.irefTable.Add(securityHandler);
      else
        Debug.Assert(this.irefTable.Contains(securityHandler.ObjectID));
      this.trailer.Elements[PdfTrailer.Keys.Encrypt] = this.securitySettings.SecurityHandler.Reference;
    }
    else
      this.trailer.Elements.Remove(PdfTrailer.Keys.Encrypt);

    PrepareForSave();

    if (encrypt && !securitySettings.SecurityHandler.MaintainOwnerAndUserPassword)
      this.securitySettings.SecurityHandler.PrepareEncryption();

...

Finally I changed the CanSave method on the PDFSecuritySettings.cs to this:

    internal bool CanSave(ref string message)
{
  if (this.documentSecurityLevel != PdfDocumentSecurityLevel.None)
  {
    if ((SecurityHandler.userPassword == null || SecurityHandler.userPassword.Length == 0) &&
        (SecurityHandler.ownerPassword == null || SecurityHandler.ownerPassword.Length == 0) &&
        !SecurityHandler.MaintainOwnerAndUserPassword)
    {
      message = PSSR.UserOrOwnerPasswordRequired;
      return false;
    }
  }
  return true;
}

This should allow you to set the MaintainOwnerAndUserPassword setting and assuming you already have a hashed username and password it should work fine and dandy,

Over and out.