After clicking on the Office button above view comes in front of us.
Click on the Protect Document/Workbook/Presentation option and then select “Encrypt with Password”.
Now set the Password to Encrypt the document. Remember the one you set here.
Reenter the password to confirm it.
Encryption completed and now when we try to open the document which you have encrypted will prompt us for the passsword in order to open the document.
Thats all !!! Happy Windows Computing.