PDFs protected by passwords are not really protected at all. There are commercially available (presumably legal, at least for some purposes) programs for "password recovery" of PDF files, which actually just give you back a password free copy of the PDF. They do this even without knowing the password. Note that a password to open a PDF is sometimes called a "User Password", and it is the harder of the two kinds of PDF passwords to recover (the other restricts printing and copying).
Since you have the password, it is possible that a 3rd party PDF reader will allow you to save a password free version without going through the "recovery" process.