You can assign a password to a spreadsheet so only those who know the password can open, read, or edit a copy of the spreadsheet.
Note: If you share a link to your spreadsheet on iCloud, you can’t assign a password to it.
To restrict access to your spreadsheet, set a password for it. Passwords can consist of almost any combination of numbers, uppercase or lowercase letters, and special keyboard characters.
Choose File > Set Password (from the File menu at the top of your computer screen), then enter the requested information.
To change a password: Choose File > Change Password (from the File menu at the top of your computer screen). Enter the requested information, then click Change Password.
To remove a password: Choose File > Change Password. Type the old password, then click Remove Password.