All versions of Windows including the latest Windows 7, file extensions are hidden by default. Perhaps it’s because Microsoft did some case study in the past and found that people don’t like being able to see file extensions??? who knows. All I know is, with hidden file extensions, it’s not easy A – Finding a file at times and B – Renaming files (specifically their extension) which is why the below Step-by-Step to configure Windows to display file extensions is one of the first things I do on new systems.
How To Display File Extensions In Windows 7
1. Right-Click the Start Orb, and then Click Open Windows Explorer.

2. In Explorer, Click Organize. Then Click Folder and search options.

3. In the Folder Options window, Click the View tab. Next Click and Uncheck the Hide extensions for known file types check box. Click OK to finish.

All done!
Now your files will show their extensions at the end of their file name. Now you can even use the Right-Click > Rename feature to change file extensions manually as well (just make sure you know what your doing first…).

Speaking of customizing Windows 7, take a look at this How-To for enabling Check Boxes to Select Folders and Files in Windows 7.
Can I get an amen!
Honestly I think not showing extensions is fine in mist cases however if your a geek and need to make a change or edit something, showing file extension is a must yeah.
It is also good when you rename files. The reason they hide is to simply things, everything is automated anyways. For old timers and programmers we got to know the extension.
[...] If you are having trouble seeing file extensions (such as .ttf or .zip at the end of the file name) read up on this groovy article for a solution! [...]
[...] Note: If you are unable to do this make sure you have file extensions enabled for Windows 7! [...]