By default, file extensions for the known file types are hidden in Windows, be it XP, Vista or Windows 7. However, if you want to see the file extensions then you can disable this feature and force Windows to show the extensions for all file types.
How to Show File Extensions For All File Types in Windows
To show the file extensions, go to Control Panel > Folder Options. Click on the View tab. this will display all the files and folders’ view settings. Under Advanced Settings, look for an option that says, Hide extensions for known file types. Uncheck this option and click on Apply.Then click on OK.
That’s it. Now all your files’ extensions will be visible. In future if you want to hide the file extensions for known file types again, then just check that option again.