This is FlashPlayer. The underlying JavaScript-like language is ActionScript which was originally developed by MacroMedia to provide animation for Flash. It's

This is FlashPlayer. The underlying JavaScript-like language is ActionScript which was originally developed by MacroMedia to provide animation for Flash. It's quite useful for creating PDF SmartForms that adjust their contents based on the user's responses. Until very recently they were only viable in the official Abobe Reader until Chrome decided to add support. As far as security, blame Chrome for not incorporating an opt-in before allowing a particular PDF to run ActionScript in the browser.