Printing secured PDFs files produece empty pages

You need to provide the password in the call to doc.InitStdSecurityHandler(). For example:

doc.InitStdSecurityhandler(“My pass”);
pdftron.PDF.Convert.ToXps(doc, xpsFilePath);

You would use doc.GetSecurityHandler ().GetUserPassword(). For the owner password (GetMasterPassword()) because the original password may be truncated or padded it may not be the same as original owner password so you should probably not rely on this method to obtain the original pass.