If your file contains sensitive information that you don’t want anyone else to see, you can encrypt the file so that no one can access its contents unless you give them the password you’ve created. You can further protect the file by allowing access to it but requiring a password to control who may make and save changes to the document, workbook, or presentation.
With your document, workbook, or presentation completed and saved, click the Office button, point to Prepare on the menu, and choose Encrypt Document to display the Encrypt Document dialog box.
Click OK, enter the password again in the Confirm Password dialog box that appears, and click OK.
Make any changes you want, saving the file occasionally, and then close it.
When you want to work on the document, workbook, or presentation again, open it and, in the Password dialog box that appears, enter the password.
With your document, workbook, or presentation completed, click the Office button, and choose Save As from the menu to display the Save As window.
Click Tools, and choose General Options from the drop-down menu.
In the General Options dialog box that appears, enter a password if you want to require a password to open the document, workbook, or presentation. Enter the password again when prompted, and click OK.
Enter a different password if you want to require a password to save changes to the document, workbook, or presentation. Enter the password again when prompted, and click OK.