[zaep]

I'm sure you're right in what you say, but this is not the reason modern acrobat is slow. I'm sure you could build a modern and accessible app that starts and loads the requested PDF snappily to show it, but acrobat will also (iirc) have some cloud integration now for storage and a bunch of the features they offer are gated behind some sort of subscription, the status of which I would guess is loaded on startup, probably along with a bunch of other stuff.