Most of the times, we want to display the file extensions, but windows is hiding the known file extensions by default.
But, if you want to make the file extensions visible every-time, then you will have to disable this default activated feature on your Windows Operating System, and allow Windows to show all the extensions whether of known file types or of unknown.
To make the file extensions visible under windows, just go to the Control Panel and hit on Folder Options. Click on the View tab.
Now the viewing settings for all files and folders will get displayed. Under the Advanced Settings panel, search for an option saying, Hide extensions for known file types. If it is checked, then Un-check it and click on Apply, then click OK.
Now all the file extensions will be visible to your computer, no matter known or unknown. Well, if you get some situation to hide the file extensions for known file types again, then Check this option (Hide extensions for known file types) again.
Enjoy!