I have downloaded a Google book as a PDF file, consisting only of page scans, and no text. The 350-page book is 18,230K, which averages 52K per page image.
No matter how I try and export a single page as an image, the resulting image is always larger than 1000K, almost 20 times larger than the original page scan.
How does Acrobat do it?
I've also noticed that if I copy a page image (right click and select copy image), then the text on the page is copied as an image, but any illustrations, are not. The illustration don't seem to be separate objects, nor background images. How do they exist?