PDF Password Recovery for Windows (Mac version here) is a fast PDF password crack tool that lets you quickly recover forgotten or lost passwords for Adobe PDF files. Below is the detailed guide on how to use this PDF Password Recovery tool
Step1. To select a lost PDF password file you want to recover the password(s) for simply press the "Open" button (or select the "File | Open File" menu item) and browse for the appropriate file.
In the Open File Dialog, select the lost PDF password file and click "Open".
Step2. Choose an attack type to recover PDF password.
There are four attack types in our program for you to recover your password. They are Brute-force Attack, Mask Attack, Dictionary Attack and Smart Attack.
Step 3. Attack settings.
Option 1: If you choose Brute-force Attack or Mask Attack, the program will try all possible combinations in the specified Range.
"Length" Settings
Minimal password length: Set the minimum possible length for the password.
Maximal password length: Set the maximum possible length for the password.
Option 2: If you choose Mask Attack, you should offer some password symbols which you can remember. A Password Mask must be defined to use Mask Attack.
Option 3: If you choose Dictionary Attack, click "Dictionary" on the tabbar.
"Dictionary" Settings:
Simply select the desired dictionary file. In addition, you can select an option "Smart mutations" or "Try all possible upper/lower case combinations"
Step 4. Click "Start" button(or select the "Attack | Start" menu item) to start the attack, then you will get your lost PDF password. 
Step 5. When you successfully recover PDF password with PDF Password Decryption, the dialog box with passwords is displayed.