You need to turn ON all of the extensions.
The default setting is NOT to show "Known" extensions. This is one of the stupidest ideas that Microsoft ever came up with.
To show all, open Windows Explorer (My Computer), go to "Organize", then "Folders and Search Options".
Then the "View" tab.
There remove the 'Check Mark', at "Hide extension for known files type".
OK yourself out and now ALL extension should be shown,