Have you tried MuPDF, Windows 8 and Windows Phone 8 WinRT component?
MuPDF.WinRT is a lightweight PDF, XPS and CBZ viewer and parser/rendering WinRT component.
The MuPDF.WinRT is just wrapper under MuPDF library (http://www.mupdf.com/), so it can support the same functions as MuPDF library
Might be helpful : Reading PDF and XPS on your Windows 8 application using WinRT [It uses MuPDF.]