• Workbook: There are a few ways to protect a workbook. You can encrypt it and protect it with a password to limit who has access to it. You can make the file open as read-only by default, requiring others to choose whether or not to alter it. You can also encrypt a workbook's structure so that anyone can open it, but they'll need a password to reorganise, rename, delete, or add new worksheets.
• You can encrypt the file with a password for added security. When someone tries to open the document for the first time, Excel asks for a password.
• To do so, open your Excel file and select File from the File menu. By default, you'll see the 'Info' category. Choose 'Encrypt with Password' from the dropdown menu after clicking the 'Protect Workbook' button.
• Type your password in the Encrypt Document window that appears, then click 'OK.'
• To confirm your password, type it again and then click 'OK.'
• You'll be taken back to your Excel spreadsheet. However, if you close Excel, it will prompt you to input the password the next time you open it.

Read More: Specify the order of operations used for evaluating formulas in Excel.