某国外 pdf 密码恢复软件的解说 When there are Document Opening Restrictions..
This is a very tricky case and there's no straight-forward solution to read PDF documents that are password-protected at the Open level.
The software will use methods like Brute Force, Key Search and Dictionary Attack to guess the password. They will try to use all possible character combinations as the password and so the process might take hours or even days and would really depend on your computer's processing power.
