Didn't know that was a thing. Built in or need a. Extension? What kind of editing is enabled(fill, sign, full edit...?) and how would you compare it to other solutions and online editors?
Things like changing, moving, or deleting text and images, inserting or reordering pages, and editing the table of contents.
There's not many open source programs capable of doing that. Pdftk and LibreOffice Draw are probably the best options right now.