What are "File" files in Windows 10?

Question

I have this weird question. If I dont specify a file extension (when File Extensions are shown) for a file in windows 10, they like... delete their extensions and are now of type "File". What extension actually are these?

Answer 1

They don't actually have an extension (since you didn't specify one), and as a result they can't be directly associated with a program to open them. Because of this, the File Explorer interface will simply display them with a generic File label under the Type column:

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This can occasionally happen when someone accidentally deletes the extension of a certain file, and the following article explains this scenario a bit more in-depth:

How to Handle Files With No Extension

What about files with no extension?

Unlike the Macintosh which embeds creator information into files so they can have just about any name, a PC still mostly uses file extensions to associate programs with files. But, what do you do with a file that has no extension? The simple answer is: punt.

With no extension there can be no direct association. So, you have to know exactly what the file's format is. You can only know this by either looking into the file and trying to figure it out or, easier, sending a note to the person who sent you the file asking what program created it and what format it's in. With that information you can determine if you can open the file or ask to have it re-sent in a format you can open.

Sources:
What Is A File Extension?
How to Handle Files With No Extension

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Needless to say, if you already know what type of file it is you can add or replace the appropriate extension to restore the file's functionality.

Answer 2

Such a file does not have a file extension. It is just the Explorer which shows "file" in detail view. For a folder (which has also no extension) there is shown "File folder".

You also could name a file "test.examplefileextension" then the Explorer will show "EXAMPLEFILEEXTENSION".