Comment by lolinder
The concern isn't that it was JS, the concern is that there's a scripting system inside of PDF at all. Why? What? Form validation is a lousy excuse because forms themselves were a bridge too far for the format. Why do we need to be able to validate them?
I knew PDFs could be dangerous, but I didn't realize it was because they're intentionally designed to allow embedded scripts.
I don't think forms are a bridge too far, it was very common that forms were provided as PDF and it is more convenient for the sender and receiver to fill the fields on a computer for readability, etc. before printing.
However, forms could be handled by a very simple DSL that would be easy to write a safe interpreter for.