I'm working with the Fire Department to make several of their forms digital. There are a few pages where we need to designate areas to draw on.
Example 1 - the page has various views of a human body: front, back, left side, right side. They need to show where burns/injuries are on the victim for an official report. The bottom layer could contain the images of the body outline, and if we could designate "draw on top of" areas, they could use their finger or stylus to identify those areas.
Example 2 - They need to provide a "field sketch" of a fire location. The background image is basic grid, if we could designate "draw on top of" for the page, they could provide this information without needing paper, then having to scan it in to add to the pdf form.