Windows 7 attempts to protect you from yourself as much as possible. A file extension is the last three (typically three, it could be more or less) characters in a file name giving the file an indicator of what program can open it. For example, a file with a .doc extension is opened with Microsoft Word, while a file with a .xls extension is opened by Microsoft Excel.  Microsoft hides the extension so that if you rename a file, you don’t accidentally erase the file extension and make the file not able to open with the appropriate program by default. The structure of the file itself isn’t changed if you change the extension, but you cannot double-click on it and open in the proper program. If you’d like to see these extensions, you can change Window’s default setting. This tutorial will show you how:

1. Click on the Start menu. Click on Computer.
   
2. Click on the Organize button. Click on Folder and Search Options.
3. Click on the View tab.
   
4. Uncheck the checkbox next to Hide extensions for known file types.
5. Click OK to show hidden files.