PDF Encrypt allows you to encrypt existing PDFs.

PDF Encrypt software is a very flexible and powerful program, PDF Encrypt software allows you to encrypt (using standard 40-bit or 128-bit supported by Acrobat Reader 5.0 and up) existing PDFs, set permissions, add user and owner password. For example you can encrypt a PDF without to allow to print it. The button to print the file will be disabled in Acrobat Reader application, you also can encrypt a PDF allowing the user to read it only if he know the correct password. Note, The source PDF must be an unencrypted PDF. Acrobat Reader will show a key in the bottom status bar if the PDF is encrypted. There two passwords you can apply to a PDF. The first is the owner password. Opening a PDF with this password will allow you full access to the PDF when a user password has been assigned as well. This means that even if printing was disabled you will still be able to print the PDF when using this password. No password will be prompted for when opening the PDF if you secure it with only an owner password. The second is the user password. Opening a PDF with this password will restrict you based on how the PDF was password protected (printing may be disabled, for instance).