Consumer confusion with trademark.
Then it would be a *trademark* issue, not a copyright issue.
(a) If my thought experiment is valid, it's legal to do it with this pdf, too.
In theory. If you get it exaclty right. Kind of like cloning a game, though, it is risky. And it isn't legal to put it up on another service for printing, because that does involve a copying step you aren't allowed to make.
(b) Bottled. Water. People buy free things all the time.
Well, technically tap water isn't free. The price is just very low, or ignored. Moreover, while most bottled waters are just tap water, it may not be (probably isn't) from *my* local tap. So, it is slightly different water. Moreover, bottled water has some convenience attached to it - sure, I can get it for (close to) free at home, but if I am not home?
Your sale of the pdf does not change the content of the pdf, or the convenience. So, what value are you adding?
So why would that apply when re-selling this PDF, but not apply when a I sell the PHB to a used bookstore for them to sell?
If you make it super-clear that you aren't WotC... and you don't use WotC trademarks in your sales, then you might be okay, I suppose. If you can survive the threat of the lawsuit that WotC might level at you. Eventually you might win in court. But you have to pay your retainers until then...
Are you trying to find that gap where something is *technically* legal, but not actually a reasonable thing to do in practice?