I am liking this tool. And this is making my Paperpile experience even better. Even if you stopped development on your PDF annotation today, I will still pay you for paperpile and continue using the annotation without more features. (Though, I will not pay you to use annotation )
Publications in my field choose not to print page numbers. Other PDF viewers have some way of giving this information, either by showing the page number on the scroll bar (when you click and scroll), or in the top toolbar as "Page 1/10".
It would be useful to have page numbering in some form, other than having to count the pages manually.