I clearly missed something, but why are you not going markdown -> PDF directly? That's what we use extensively in our operations playbooks at work and it gives something that looks like I'd get in a book - even more so after I tweaked the templates a little.
Because the user in question does not know and is unwilling to learn how to design anything if it is not web technology. That is, you probably want to design PDF output. Some users prefer to do any design work whatsoever using web technology. Therefore, PDF needs to be generated from HTML.
In fact, he's not even aiming to design a professional-looking PDF document, just a throwaway printout for proofreaders who don't know how to parse Markdown.