From LastBit Software:
Utility to recover lost passwords to password-protected PDF files (*.pdf). PDF Password recovers user and permission passwords only. PDF Password does not allow to break DRM (Digital Right Management) system. If user password (also known as password to open) is either not set or known, it is possible to remove permission password instantly. Unfortunately, if a user password is unknown, there is no easy way to recover the password to a PDF document. Universal recovery methods, such as Brute Force Attack and Dictionary Search, must be used. Unfortunately, due to a nature of an encryption method used in PDF files, the password search is very slow. The brute force speed is usually under one thousand passwords per second even on a top-speed modern PC. The recovery methods used by PDF Password: Brute Force Attack, Dictionary Attack, Smart Force Attack, Password Variation, Reset password (only if user password is either not set or known).