I wouldn't say PDFs are bad for visually impaired users. In fact, as bitmap fonts are thankfully a thing of the past for almost everywhere, you can zoom any document to your hearts desire. Though sometimes you need some tricks, e.g. Evince is configured to only use 50 MB of storage by default for caching, vastly limiting zoom capabilities. So you'll have to dig into dconf to change that.
What you are looking for is ways to reflow text, but as a fixed layout format, PDFs are just not meant for that. Not even the PDF/UA standard [1] does require this, it only lays the ground rules for screen readers. Supposedly the swiss-made "VIP PDF-Reader" was able to help, yet it seems to have been abandoned as there doesn't seem to be any download options anymore. And other than that, PDF readers with that capability are very rare on any platform. No idea if anybody besides Adobe is doing that because PDF is such a terribly complicated format. In theory, this should all be doable with Tesseract, as it already does the OCR part. Just nobody has bothered yet to support such use cases yet and support an output format that can even handle more than just text. Best Richard [1]: https://en.wikipedia.org/wiki/PDF/UA
