I often find myself in the need to work with different literature about the same topic.

It would enhance my work a lot if I could link related pages of a document A to a page in document B, as B may give other/more explanation or vice versa.

Therefore a linking annotation would be very interesting:

* Place the link on a page or draw it over some text
* a dialog would open:
** let you choose a URL or a different document:
** if it's a PDF document, it would open the document (or change the tab if it was already opened in Okular), and let you choose the desired place to place the "other end" of the link.

That way you could go back and forth between two or more documents in the case they cover similar topics.