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.
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.
Select the checkbox if you want to add the password to your keychain.
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.
Remove a password: Choose File > Change Password. Type the old password, then click Remove Password.
If the spreadsheet is being shared on iCloud, you can add, remove, or change a password in Share Settings.
Note: Adding a password to a spreadsheet doesn’t encrypt the file.