Error 70 is a permissions error. If your error message indicates otherwise,
let us know. But this sounds like you do not have permission to open the
file for some reason. Either you don't have permission to the folder the
file is located in, or (if you're trying to open it in code) you haven't
provided the password needed to open the file within the code statement
opening the file.
Go into Windows Explorer and find the file, right-click on it and choose
Properties and see what that tells you. It may be marked as Read Only,
although usually if that's the case you can open it, just have to save it
with a different name to save changes made to it.