Adobe PDF functionality

[Binary91]

Hey,

I'm trying to write a program to handle pdf files. The program should be able to open pdf files that are password protected. So I need functionality to encrypt a pdf.

Do I need special PDF libraries for my purpose?
If yes, do you know some good libraries that are free for download?

If no, how can I access pdf files that are password protected (I know the password, I only need a function to encrypt the file) ?

I'm using c++ and my OS is windows 7 (64bit).

Thank you in anticipation!