PDF supports not only images but also: video, audio and 3d models. I see we have only images in JSS. It is possible to embed all this in other document types, not only PDF.
Why we need it?
Imagine airplain, tickets you recieve by email in pdf format where you have some video instructions or a 3d model which will help you find your seat in the airplane.
Imagine a manual or prescription in pdf format you get from your doctor where you have a 3d model or video inserted which will help you understand what you have to do.
We are in 2020.