Once a Gradebook has been downloaded, it is strongly recommended that is is assigned a password for protection. This document shows how to set a password for Office 2011 on a Macintosh computer.
Select Save As from the file menu.
Click on the Options... button.
Enter a password in the Password to Open field and click OK.
Re-enter the password to verify.
Next, click Save.
To delete files so that they cannot be recovered choose Finder then Secure Empty Trash.