Uber Techy

In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename EDIT.DOC, the extension is DOC, which indicates that the file is a word processor file.

in Registry you can see the programs used to open the type of file they are called File Extension [e.g .doc .exe .vbs .cpp] in registry File Extension
are treated as part of an application since you need a certain app. to open the file. chances are continuous installations of programs that can read this can read that, the registry wouldn’t recognize what apps to use to open a certain file since your PC has a tons of picture viewer for example.

There is a fix for that it is called registry cure it solves your File Extension problems