The file extension (normally hidden) can be viewed quite easily, sometimes it is handy to see it so that you can treat the file in a particular way.
To view it first open FILE EXPLORER and click the VIEW tab, then look for the checkbox towards the right that says FILE NAME EXTENSION.
When you tick that box, all the files that you see in File Explorer will become visible.
Solved: How to show the file extension in Windows
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It’s quite useful to know some of the common extensions, as sometimes things can go wrong and you could find the wrong program opening or worse! Read these articles for more: