Click the File menu, select the Info tab, and then select the Protect Document button. Click Encrypt with Password. Enter your password then click OK. Enter the password again to confirm it and click OK.
Zipping and putting password is the same?
If you put the files you’d like to protect in a zip file, you can then apply a password. In Windows Explorer, highlight and right-click on the files you would like to put into a zipped file. Select Send to, then Zip folder and make sure to compress. Double-click the zipped file, then select File and Add Password.