I am an author (not of this book) and I very occasionally get an email asking for PDFs. Maybe one in a thousand sales are PDF. Since it doesn't come up that often I've never bothered with setting up a paid system; I just send them a link and ask nicely for a few bucks via PayPal.
Where do most people go to buy PDFs? Is it really a large-enough market to worry about?
Lulu? At least that's the only place I've specifically bought a PDF - then I found out that it's wrapped in some horrible Adobe DRM (if there are any ways to remove this, I'd love to know). I don't begrudge the money, I just wish I could read it in Preview.app rather than Adobe Digital Reader or what ever it's called - it doesn't scroll smoothly, only page wise which is a massive pain when there's lots of diagrams.
Other than that, all the ebooks I've bought from individual storefronts, often from having seen them on HN, have come as a PDF/epub/mobi bundle to work on any device.
Please don't password protect PDFs for books. It makes it a huge pain in the ass to actually read. I'd much rather you do what the Pragmatic Bookshelf does and just embed our name into the PDF.
Don't know, but I find it a great way to read on laptops & desktops. Of course, a nice html would work as well, but that's rare. (also, the pdf reader in KDE remembers what page you're on and lets you annotate etc..)
Where do most people go to buy PDFs? Is it really a large-enough market to worry about?