When is the last time you had to pinch and zoom on a website? Text can reflow perfectly well, if you give the renderer the necessary information. With PDF, similar to PNG, you're specifically telling the renderer to put this pixel exactly over there and nowhere else, so it cannot nicely make it all be readable comfortably.

If mobile devices required zooming and panning to read anything, they'd not be popular at all, so they're apparently not where the problem lies.

A4 is the issue. Mobile friendly pdfs could be done, just stick bigger text on each page like a kindle does.

But then you have super narrow views on desktop, we don't want that either. What's wrong with just using the formats we already have for reflowable text, why bother trying to make PDF into something it's fundamentally made not to do?

Yeah good point. I think it’s that adobe stranglehold. “Never got fired for…” kind of thing.