Add a cover image to the icon - embedded image?
I am sure this has been asked before, but maybe I don't know the terminology.
I have a fair few books I have downloaded from various places. Below is an image of a few official GamesWorkshop books I have bought. They all have cover images.

However, any PDFs I create just show the generic PDF icon. This test PDF has an image as the first page.

However, this isn't an issue with turning on "Enable PDF thumbnail previews in Windows Explorer". When I enable that I see this:

This is clearly a preview because there are white bars to either side of the blue image.
So how do I set an actual cover image like all those professional books?
