Encrypt PDF

At first, select PDF file to encrypt. Then input user password and/or owner password ( N.B. Password should not contain quotes. Then select encryption method and features that will be allowed/forbidden. Features to be allowed should be checked, features to be forbidden should be unchecked.
For more information, please see pdftk help.
You can overwrite input file with encrypted one.
To do so, select 'No' when asked whether you want to create new file.