I routinely have to open large spec sheets for work. Have you ever tried to open any large documents with PDF.js? Chrome's pdf plugin can handle 100+ page documents with ease, while Firefox's PDF.js can make the entire browser unresponsive. Hopefully e10s will finally fix this.

Agreed. PDF.js and multi-process both have room for improvement, but the security benefit is huge.

Ideally, NPAPI and Pepper should both die, but I don't necessarily mind them killing NPAPI and adding this minimal set of Pepper support for Flash. Pepper crashes the browser less (though most of the fault lies with Flash).

But even if this enables PDFium, it should not be adopted, and the talk of adopting it makes me want to oppose the whole idea of "project mortar."

I haven't used Chrome in a while, but I seem to remember being able to use pdf.js in Chrome by installing an extension.