From ~30s of searching, it looks like that's an Adobe Reader feature: https://stackoverflow.com/questions/9219807/using-javascript...

My original comment was going to be "Who thought that was a good idea? Maybe there are reasons, but that sounds like a terrible idea at face value".

Chrome's builtin PDF reader supports it. You can even find a PDF that uses JS to play a game of pong in Chrome.

Well, out of all the places that makes sense, it's Chrome after all.

Either way, it sounds like a pretty bad idea to add this as a feature to Adobe Reader or somehow to the PDF spec. Especially since PDF remote code execution exploits happen relatively often.

I've seen some forms made with PDFs with js in them. A painful experience for sure.