This is usually an indication of amateur scanning, or inadequate software ... or both. :nono
I'm not sure when the BMW manual was scanned but I'm guessing it was many years ago. It's not a very good scanning job but the pages are straight. I'm not meaning to disparage the freebie from the mothership, just sharing my thoughts. I reprinted some of the pages on our color printer at work, using grayscale, and they came out much better than our B/W printer. I'd still like more detail but unless I can buy a print copy of said manual. :dunno
I bought what I thought was a printed copy of the manual on eBay before I found the pdf and I swear they printed it using microfiche because the dark and light all seem reversed. It's the worst $25 I've ever spent. lol