Individual Document icons on Windows

I notice that PDF files which I generate in Windows are now getting ‘preview’ style icons, associated with Foxit Reader.

Ive been doing that for some time on the Mac myself, using an MBS plugin.
But I always thought that the icon on Windows was firmly associated with the file extension, and therefore all PDF files (for example) would show the same icon.
Thats clearly no longer true.

Does anyone know how to make an individual file have an icon that differs from another file of the same extension?

update: some reading later, it can only be done using a COM DLL that presents an IconHandler interface
Xojo cant make them, and I don’t have a C# setup to play in.

Any other suggestions welcomed if there are any?