Note: All Excel protection is relatively weak. It is useful to stop casual users but it is not for top secret information.
If you want to have more control over the people that can open the file and only view it versus people who can open the file AND make changes you need to add a Password to Modify.
To follow along go to 19.2
When you choose the File Save As option you can include a password to open and a DIFFERENT password to Modify.
All the options work by either entering your password into the appropriate block or ticking the appropriate box. If you enter a password it will ask you to confirm it when you press OK.
If you enter a ‘Password to Modify’ then the user needs to know this password to be allowed to make changes and save over the file. If they don’t know the password they need to open it as Read Only and if they try and save, it will suggest they rather save a copy.
If ‘Password to Open’ and ‘Password to Modify’ is completed, when it is opened, the user would need to complete both to be able to modify it. If they only fill in the Password to Open then it will open as a Read only.
A less secure but good option is to tick the ‘Read Only recommended’ (with no passwords although you can use a password if you want). In this case when the file is opened the person has a choice whether to open it as a Read Only or not. If they do open it as Read only they won’t be able to save over the existing file, only make a new file.