Have you ever had a file on your computer, maybe one someone sent you, that you did not recognize the extension or know how to open? I'm not sure how they get on my computer, but I have had them in the past.
What I normally do is to just do an internet search for the extension (that would be the three characters after the dot at the end of the file name) to learn what program created and/or uses the file.
Sometimes the programs are "for pay" and I'm stuck. Sometimes I can download the program.
I want to make note that sometimes those stray files are spyware or other nasty programs, so DO NOT CLICK until you research them. That is always a good practice to follow.
I found OpenWith.org which is a great site you may want to add to your bookmarks.
OpenWith provides detailed information about most file extension and links to free programs that can open and create each type of file. There are times when a free program is available to open a program, rather than the paid version.
There is also an OpenWith Desktop Tool which looks great, but I see no need to install it. I do not need more programs taking up room on my computer. For as many times as I would need the service, I would prefer to just go to the website and click on the suggested program to download, rather than having it on my computer to do it for me.