If there is no program set as the default application for opening a file type, when you right click on a file of that file type and choose Properties, you will see "Pick an app" next to "Opens with".
If you wish to identify all of the extensions known by the system,
you can use the assoc command. If you type the command
at a command prompt with no parameters, you will get a long list.
You can redirect the output to a file with assoc > list.txt
or page through it by piping the output of the command to the
more command with assoc | more.
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