|Well, there are other ways to do this, just not from Excel.|
File auditing can be turned on, and you could get some program scan the audit log to see if the file has been modified, and send an email if it has. The email would not happen until the program ran and noticed a change in the audit log.
Some program could register for file change notifications and send an email when it received a notification that the file changed. The email would be sent immediately, but Windows doesn't guarantee you'll be notified of file changes.
Neither of these options would detect someone copying the file and modifying the copy, but that's how it goes.
How To Ask Questions The Smart Way