How to Set a Document-Open Password in Excel

To configure your workbook so no one can open it without a password, apply a document-open password in the Info area of Excel.

How to Add a Modify Password to Your Excel Workbook

Another approach to protecting an Excel worksheet is to apply a password to prevent people from making changes to it after it is open. It becomes read-only for anyone without the password. Your workbook is now protected from anyone opening it if they don’t know the password.  If they enter the password incorrectly, Excel lets them attempt to enter it a second time. If they fail to enter the correct password again, the worksheet won’t open. This is the best method to secure your Excel files.

How to Protect Password Structure During Review

If you frequently review draft workbooks that people create, password protecting the workbook when it’s in the review phase is a good way to prevent changes during a quality review. This doesn’t prevent content changes, but it does prevent people from adding, removing, renaming, or creating new sheets. It protects the structure of the workbook itself, rather than the contents.