Protect. Encrypt an Excel file with a password so that it requires a password to open it. 1. Open a workbook. 2. On the green File tab, click Save As. 3. Click on the Tools button and click General Options. 4. In the Password to open box, enter a password and click OK.5. Reenter the password and click OK.Note: this feature also encrypts your Excel file. If you lose or forget the password, it cannot be recovered.6.. Click on the Tools button and click General Options. 4. In the Password to open box, enter a password and click OK. 5. Reenter the password and click OK. Note: this feature also encrypts your Excel file. If you lose or forget the password, it cannot be recovered. 6.