We get this question a lot from users who already have Adobe Acrobat 9 Professional and are curious about how to password protect their PDF document. Follow the short and easy tutorial below.
Protect PDF Document with Adobe Acrobat 9
Launch Adobe Acrobat 9 Pro, if you haven’t already. Then open up the PDF document you are wanting to protect.
Click on the “Secure” menu link, and then select “Encrypt with Password.”
Then in that window you can choose “Require a password to open the document”.
And that’s it!