By default file extensions may not show in Windows Explorer. In case they are not showing follow the indicated procedure.
You may just know the file name in the Windows Explorer. Sometimes you need to know the correct extension. This is especially true when you rename a file. It is true that the icons may change and you may know the difference. But you may change the default of not showing extension to one showing extension by following the indicated steps:
In Windows Explorer open in C:\ drive
1.Click Tools | Folder Options...
2. In the Folder Options window change to the View Tab
3. Under Advanced settings: ,remove the check mark (default) for the radio button Hide extensions for known file types.
4. Click OK to the Folder Options window.
Now your files will be showing the extensions