[docfort]

I think Lockdown would help here since it doesn’t decode message attachments. So the original link in the chain (decoding a PDF) would be impossible.

As for detecting unauthorized apps, I would imagine that once you’ve taken over control of the OS kernel, it’s game over for such software-based restrictions. The Halting theorem guarantees such limitations to any software-based restriction. And as long as you can form a Turing complete mechanism from pieces of the computer, such software limitations will apply.