If you’re using Excel 2007 or later, the option to require a password to open an Excel spreadsheet may be in a different place than you are used to in earlier versions of Excel. Follow the steps below to require a password to protect your spreadsheet.
Step 1: Choose File -> Save As.
Step 2: Enter a filename, and click on ‘Tools’, just to the left of the Save button. Then select ‘General Options…’.
Step 3: In the box that opens, enter your chosen password in the top box. Note that there are two passwords here - one to open the spreadsheet and one to modify (but anyone can open). We’re setting the former - to require a password to be able to open the spreadsheet, but you can do either (or both).
Step 4: Excel will give you a warning about the consequences of forgetting your password and prompt you to re-enter the password to confirm it:
Step 5: Then choose a filename and save as normal. You will see the following when you next open it, requiring the password you entered to open:
Note that password protecting a spreadsheet might make it difficult to open in other programs, web services (e.g. Google Documents / Gmail attachments) and mobile devices.