Protect a workbook
To prevent a user from accidentally or deliberately changing, moving, or deleting important data from a sheet or workbook, you can protect certain sheet or workbook elements, with or without a password. You can remove this protection as needed.
Passwords in Excel for Mac and Word for Mac have a 15-character limit. You cannot open a workbook or document that has been password protected in the Windows-based version of Excel or Word if the password is longer than fifteen characters. If you want to open the file in Office for Mac, ask the Windows-based author to adjust the password length.
Sheet and workbook element protection should not be confused with workbook-level password security. Element protection cannot protect a workbook from users who have malicious intent. For an additional layer of security, you should help protect your whole workbook file by using a password.
Do any of the following:
Protect workbook structure or window size
Protect and share a workbook