In Window 7 file extensions are hidden by default and you might want to change the extension of any file. T0 show file extensions in Windows 7 follow the few simple steps.
Double click on Computer icon or click on Start button > Computer
In the explore click on Organize > Folder and search options
In the Folder option windows click on View tab and then under Advance Settings uncheck the option Hide extension for known file types and click OK button to save the settings
Now you notice that all file extensions are displaying after the file name