that's the power of legacy. Adobe may think they can add junk to PDF like Javascript support, or lmz's "3D PDF" link below, but since PDFs viewers have a diverse ecosystem, those features won't have a great adoption.
And this is actually pretty great, maybe even the best part of PDFs! Companies _know_ that publishing PDF that require 3d-graphics or Javascript means many people won't be able to see them, so they publish good, static PDFs, maintaining virtuous cycle.
> (4) won't require Javascript or access to external sites
So about that... https://opensource.adobe.com/dc-acrobat-sdk-docs/library/jsa...