Office Document Encryption
Microsoft Office has a built in facility to encrypt Office documents. This facility can be used to encrypt all Office files, including spreadsheets and presentations.
To protect a file in this manner, simply click on “Protect Document” in the Info menu and click on “Encrypt with Password"
Enter a password of your choice here. You will need to provide this password whenever you wish to open the Office file. To ensure your data is properly protected, choose a strong password.