Software by PDF Unlock:

The standard security provided by PDF consists of two different methods and two different passwords. A PDF document may be protected by password for opening ('user' password) and the document may also specify operations that should be restricted even when the document is decrypted: printing; copying text and graphics out of the document; modifying the document; and adding or modifying text notes and AcroForm fields (using 'owner' password).

PDF Password Cracker Professional edition allows to search for "owner" and "user" passwords with brute-force and dictionary attacks, effectively optimized for speed (however, don't expect to recover long passwords in a reasonable time with these attacks). In addition, it has Key search attack, which guarantees the decryption (regardless the password length and complexity) of PDF files that use 40-bit encryption.