Even better, every font renderer does! A couple of the PDF-based jailbreaks for iOS were actually bugs in the virtual machine used by font renderer to allow fonts to do programmatic hinting, and the PDF only really existed as a container to deploy the font and force it to deterministically render exactly what was required.

I intuitively expected some trash like that from Adobe which is why I wrote "every PDF viewer" and not "Acrobat Reader".

Prompts are not opt-in. Opt-in is moving the mouse to (say) the lower-right corner, clicking on the NoScript icon, and selecting "Temporarily allow example.com".

That's not a panacea, but it at least raises the bar from "get people to even briefly look at your attack site", to "come up with a at-least-vaguely-plausible excuse why your site needs to be handed a remote code execution vulnerability in order to function".