Where are the regions? Demo
pdf.js draws the page. Every region the map reads from the file is boxed on top of it, one colour per kind, and listed beside it in drawing order. Hovering either one lights up both.
This demo needs JavaScript. It reads a PDF you choose in this page, with nothing uploaded, draws each page with pdf.js, and boxes every region the map finds in the file.
Blue boxes are lines of text, green ones images, purple ones drawn shapes and orange ones annotations. The write-up explains how it works and how it was tested.