Comment by async5

There are not exploitable (at least not the same way). Firefox PDF viewer is a modification of PDF.js, so PDF.js code would run in the browser without a web server. The exploit might poke a hole in EMBED tag security of the web browser (and not in the PDF.js code itself). WP plugin shall be safe as any web application (unless it introduces similar security hole in its code, e.g. XSS).