Document Protection Password

Hi,
What is the password used for protecting a document? Is there a way to change this so only certain users can unprotect the document?

Thanks!

We don't have the algorithm MS Word uses to convert from a password to hash. Only hash of the password is stored in the document. We protect the document with a random hash. We don't actually know the password itself.

I would not rely on protecting the document with a password in MS Word since it is always easy to unprotect it. Save the document in RTF or in WordML, remove the password using Notepad and open in MS Word again and the password is gone.