Its not possible to use tools from the iPad with Nav, its only possible to select them. You should be able to view open documents on the iPad in Nav in either full screen or thumbnail mode. To go from thumbnail mode to full screen mode, just use zoom in/out gestures (place two fingers together on the thumbnail and then move your fingers apart or together). Double tap the screen to exit full screen and then zoom out to return to the original thumbnail view.
Adobe Nav is often used for setting up a commonly used tool set on the iPad and then being able to quickly select any tools there versus within the application itself. Also, if you work with a lot of open documents, the open document view
allows you an easy way to bring certain ones to the front.
I found this overview video from the designer that talk about the app. It might be helpful.
Hope that helps,