There are many reasons why you want to encrypt your PDF documents. But what is the simplest way to achieve it? Here, we could like to strongly recommend Coolmuster PDF Encrypter for your reference. With it, you can encrypt your PDF files anytime you want.

* Set User Password (Open Password) to PDF to prevent PDF from opening directly.
* Add Owner Password to a PDF document to protect PDF from reuse.
* Support 3 different encryption systems: 40 bit RC4, 128 bit RC4 and 128 bit AES.