Comment by kragen
Adding JS to PDF seriously undermines these benefits. If Turing-complete logic can draw arbitrary images on the document, you can no longer have any print fidelity at all, and what you signed cryptographically may have said things you didn't know it said. It may start interfering with #1 if email systems start blocking "malicious" PDF features, too. Only benefit #2 survives.
I have no idea what the folks at Adobe were thinking when they decided to add this feature that could eventually eliminate most of the benefits of their product.
None of this is to say that the Doom implementation is anything less than a very cool hack.
probably the same thing that netscape did when adding javascript to the web. "now we can add some basic client-side validation to these forms". PDFs can be used as form templates, so having some basic validation is reasonable.