I’ve got 70-80mb pirated books, I think because of the illustrations. Guess it depends on the book.
You clean up the data after you acquire it, not before.
Discounted Seagates ? /s
Other times a PDF of a book is big because someone scanned it and didn't have trustworthy OCR, so they figured distributing images of text at 1.5 MB per page was better than risking OCR errors.