I can't think of a way to password protect a text file. However, you could use the File Attribute command to mark it as read only. This would allow them to look at it, but not modify it unless they go into the properties and remove the Read Only flag. This is not a true solution, but more of a deterrent.
You could also use the File Attribute command to mark the file as hidden. Again, not a true solution, but it would hide the file unless they have the Show Hidden Files option selected in their File Explorer.