In addition to setting a password to open an Excel spreadsheet, you can set a password to allow others to modify the spreadsheet. Click the Microsoft Office Button, click Save As, and on the bottom of the Save As dialog, click Tools. On the Tools menu, click General Options. The General Options dialog opens.et a password in an Excel spreadsheet. To encrypt your workbook and set a password to open it: Click the Microsoft Office Button, point to Prepare, and then click Encrypt Document. In the Password box, type a password, and then click OK. You can type up to 255 characters.