[morecoffee]

The PDF reader is pretty interesting, because don't modern browsers ship with PDF readers? To decode the embedded JPEG2000s, the browser has to be able to decode them right?

[tinus_hn]

PDFs are packaged Postscript. Postscript is a Turing complete language and the output of a script is a page.

PDFs with JPEG2000 images contain a Postscript library to decode these images. That is the code that gets to show them.