You can make Excel always open old spreadsheets in Protected View. Enable or disable Protected View using in-built setting, Group Policy, Registry.

With the Excel file open select File in the top-left corner of the screen, followed by Info. Select Protect Workbook, then choose Encrypt with Password.

There are several options available to you to protect your Excel file with a password. Remember that once you protect the Excel file, you cannot open it without entering the password.

However, if you open a protected Excel file in the browser edition, you can see hidden formulas, but you can’t modify them. For most sheets, hiding formulas is overkill but easily implemented.

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