Tools - Locking

Ribbon bar. Select the Tools tab. Click Locking...

Classic menus. From the Tools menu, select Locking...

...to display the Lock Spreadsheet dialog box. Using these options, you can prevent changes to spreadsheet data, display elements (e.g., fonts and formats), case selection and weights, audit trail options, and/or variable specifications. You can also specify and confirm a password. When the password feature is in use, only authorized users (i.e., users who know the password) can modify the locking conditions and the locked spreadsheet.

Locking vs. password encryption. Note that spreadsheet locking makes portions of the spreadsheet read-only, enabling you to prevent changes to some or all aspects of the spreadsheet. The spreadsheet can be opened by anyone, but locked portions cannot be altered. Use of a locking password is recommended but not required. To password encrypt a spreadsheet so that it cannot be opened without the correct password, select File - Properties to display the Document Properties dialog and enter a document password on the Password tab. Only users who know the password can open the spreadsheet. Once a password encrypted spreadsheet is opened, it can be modified.