I was checking out Qubes' way of creating safe PDFs, but unless you use Qubes as a daily driver (and use DispVMs to open PDFs) it's still not viable to just use it to create image-based PDFs if you have very huge documents in them. I really hope they someday manage to find a way to create safe PDFs without the increase in size and loss of functionalities. If there already is a way, please tell me, but until then I was considering other options.
As far as I could see, the least risky readers to see PDFs in should be the browsers' embedded PDF readers, as they can use browser sandboxing and they're pretty simple as well. On the PC I guess opening PDFs in Firefox/Chrome/Edge should be the way then. But what about Android and iOS? The browsers for them don't have an embedded PDF reader. What could one do to have at least that sort of security on those OSes?