I would pay at least 10$ for an app that made an aesthetically-pleasing HTML flow of any pdf document I’m looking at. At least. And I can’t imagine I’d be the only one. So much of my reading is on-screen now, and PDFs do kind of suck for two column reading.
It definitely feels like a one time payment, since my mental model for it would be “pdf reader.” Also, since I’m accustomed to SaaS in my business dealings, but detest it in the private consumer space, and this would appeal to me as a consumer; my business documents are already mostly PowerPoints, with the occasional word doc.