Version: 0.9.2 (using KDE 4.3.2) Installed from: Unlisted Binary Package The [alt]+[left arrow] and [alt]+[right arrow] key combinations should work by default; possibly in addition to that, also [Backspace] for "Back". These are very widely known and used shortcuts. You shouldn't have to configure them manually (just as you did't have to in kpdf, nor in any other modern browser-like application that has this kind of Back/Forward functionality).
Will be fixed in kde 4.4, using alt+shift+left/right instead of alt+left/right because that are reserved for konqueror history