How to protect and add password to pdf file before sending via email?

Is there any way to add password to pdf documents before sending as an attachment via email? Any way to do that? It is necessary to add password to pdf file in order to protect the document security. Any help will be appreciated!

Some people recommend me to try Adobe Acrobat Pro tool to lock my PDF files with password. However, as we all know, although Adobe Acrobat Pro has a built-in feature to lock PDF files as well as set security restriction to pdf file. But it is so expensive, I can not afford it. Any cheaper software?

Then I found a tool called WowTron PDF Encryption, it is a powerful pdf encryption software which enables users to lock pdf document with user and owner password. It also allows users to add restrictions to pdf documents. Recommend to use WowTron PDF Encryption, know more details, visit here: