How do I show or hide file extensions in Windows 7?

(View instructions for Windows 8)

By default, Windows 7 hides file extensions for known file types such as .TXT and .JPG. However, you can change this setting through the Windows 7 Control Panel by following these steps.

From the Start Menu, choose Control Panel.

Start Control Panel

Next, select Appearance and Personalization.

Appearance and Personalization

Click on Folder Options.

Folder Options

Lastly, uncheck the option for "Hide extensions for known file types" and click OK.

Hide Extensions

Windows 7 applies this option globally to all folders, so you will now see common file extensions such as ".txt" and ".jpg" displayed in each folder. If you want to hide file extensions in the future, you can simply recheck the same checkbox.