It is pretty clear if only one page is visible but if multiple pages are visible, how can you tell which page the user clicks on? I looked through its properties and nothing really stuck out. Even if I find a way to show only one page at a time, it would be ok.
I did an input hit test and turned that into a FixedPage. If this was null, obviously a page was not clicked. Then I went through every FixedPage in the DocumentViewer and found the matching page.