Why does the file type not change when converting a .PDF to a .PNG?

Question

I was watching a video where the narrator stated that changing a file type from .PDF to .PNG doesn’t change the actual file type of the document. Could anyone explain why ?

In: 2

Answer 1

Changing the end doesn’t change the format of the document just what the computer sees as compatible softwares to open it with

So it may try to open it as a PNG but the contents will still be PDF and this may be unable to open it

Essentially if you see PDF as a square object and PNG as a round object changing the end is just you telling the computer this is a round object and so it gives you a round hole but the document itself is still square