Can a file be password protected using Adobe Acrobat XI Standard? No one seems to have answered this question in the trending questions.

I just purchased Adobe Acrobat because it was recommended to password protect files.

However, when I checked out the Tools > Protection > Encrypt>  "Encrypt with Password" is greyed out.

Can a file be password protected using Adobe Acrobat XI Standard?

The OS version is Windows 7.

No one seems to have answered the question in the Trending Questions.

Thanks.