[RogerBW]

There are two different things potentially going on here, each of which can be useful in the right situation.

(a) Take a PDF page (containing text, vector graphics, and/or bitmaps) and render it into a bitmap.

(b) Extract an individual image from the PDF, and use just that bitmap.

For example, I'm using some Pathfinder adventures at the moment where the basic dungeon plans are pretty bitmaps, but all the labels have been added separately in the PDF – which means that if I extract just the bitmap I have a tactical map I can add a hex-grid to and show to the players, without having to hide all the annotations.