We've been using the proofing feature since it's come out, and love how easy it is to use. I mentioned in another post some visual glitches, but otherwise it's been really great to use.
After spending more time working with it though, after revisions are made to the PDF, there isn't a way to update it with a new file. We have to attach a new one which becomes confusing to maintain a bunch of version within the task.
So, we've been deleting them—but that also remove the comments attached to the PDF and now we've lost all history of task revision history.
Simply put, we need a way to replace an attachment with a new version and have the comment history remain intact.
That's an immediate need.
This can be taken even further with having a "version history" of each attachment and having comment bound to the "versions." But I recognize that's a much bigger ask and will take more time. So, I'd like to request specifically the "replace file" feature as a short-term/immediate solution and the other as an eventual feature (when you get around to it—not pressing).