Sometimes you have to check a paper a few pages above the current page to compare stuff (for examples equations). For this it would be nice if a SplitView exists, which displays multiple documents side by side (regardless if it is the same or not). 

The benefit of a splitview instead opening the document twice is that when you change something in one paper it is directly visible in the second one, without reloading the paper (when you have two view, but only one model). 
Also you can use one pen for writing notes down.

What do you think about?