When opening any document, especially with PDFs, it would be great to have the possibility to have a separate page on the side to take notes. This page on the side sticks to every side in the notebook while scrolling and is not included while exporting.
Especially for students, this would matter a great deal. Because, for example, we have the slides which the professor gave us in our main document inserted, and then he talks and talks. One has to write down all the stuff the professor just said down, but it isn't possible within the slide because there is no more space. Inserting a new page under it isn't really helping, then you have to scroll up-and-down all the time.
All together, it would be really nice to have a sheet of paper right next to the pages of a notebook to take notes.