> But there are two killer features that most annotation software fail to supply:

I don't know what kind of annotation software you usually use, but I have yet to annotate a PDF and lose the ability of 1 and/or 2.

As for crowd-annotation services, I can only think of genius and medium. Genius does not preserve original format, but that is obviously unreasonable to expect (they're songs!). Medium is its own format, so rendering is accurate by definition.