A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
Hi Tom,
Hopefully, I understand your question better than your source and Waqas.
Waqas explains various options for protecting a worksheet but unless I am mistaken, your question asked how to protect an Excel workbook file, not a worksheet.
Based on what you asked in your question, I think you might be after the way to require a password to open the file. That's found by using the Menu Bar and choosing the File menu > Save As dialog.
Click the Options button to display the Save Options dialog where you can enter a password to protect the workbook file.
Did I understand your question correctly?