I've been using Sumatra for some time now and I really like the fact that it's fast and lightweight. If I may, however, I'd like to suggest 2 features:-
Ctrl-A selects all text (where present) - just like in Adobe Acrobat. This would be great for copying all text in a PDF to another document. In Sumatra it currently selects the whole page, which may be not as useful (nothing much one can do with that).
Hovering the mouse cursor over the file tab causes the full name of the document to appear as a tooltip. This is very useful when opening many documents in a tab. Right now the only way around it is to set Sumatra to not use tabs, which causes too many windows to open.
Many thanks in advance for considering!