HelpWindows7.com

[felix]

I have recently installed windows 7 on my PC and found that by default in Windows 7, known file types are set to hide.

[gabriel]

Here are some steps
Open Folder Options, and click on the View tab.
Uncheck the Hide extensions for known file types box-> OK

[bonaventure]

You can also do this through Registry Editor
1. Start->Run->Type" Regedit"
2. Locate the following
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
3. In the right pane of Advanced, Rt click on HideFileExt and click on Modify.
4. To show the file extensions Type 1, and click on OK
5. Close Regedit