Are you a developer? Do you want to add "PDF Encryption", "PDF Protection", "Add the owner & user password and restrictions of PDF files" feature to your application?
Now, you can try PDF Encrypt ActiveX DLL, with a few function calls, it helps you encrypt pdf in your Win programs or Web applications.
PDF Encrypt ActiveX DLL was intended to protect Adobe Acrobat PDF files, that comes with "owner" and "user" password set, preventing the file from editing (changing), printing, selecting text and graphics (and copying them into the Clipboard), or adding/changing annotations and form fields.
All editions of Adobe Acrobat (including 5.x, 6.x, 7.x, 8.x, 9.x which tools 40-bit,128-bit RC4 & AES, 256-bit AES encryption) are allowed by PDF Encrypt ActiveX DLL.
It is a standalone component and does not depend on Adobe Acrobat, or even Acrobat Reader.