Even when you tell your computer to show all file extensions (by unchecking the Hide file extensions for known file types) there are a small number of extensions that still don't appear. These files are mostly system related ones such as shortcuts (.lnk) and scraps (.shs).
For more complete knowledge of exactly what type of file you are opening it would be useful to have these extensions showing as well. After all you don't want to go opening what you think is a text file and find that it was really a shortcut to an executable program (virus or trojan).
Making these remaining extensions visible is not as simple as for the others, you'll have to edit the registry to do it.To edit the registry run regedit from the run option in the start menu.
Each of the hidden extensions has a registry entry that tells the operating system to hide the extension. These registry entries all read NeverShowExt so if you do a find for that you will find those extensions that are always hidden one by one. If you remove that registry key then that will make the extension visible.
Note that I recommend that you back up the registry before attempting to make any changes to it.
This article written by Stephen Chapman, Felgall Pty Ltd.