In my application, in the pdf viewer, I want to superimpose a video/audio file at specific coordinates in the pdf file.
Please have a look at this forum post: https://groups.google.com/d/msg/pdfnet-sdk/jZf5OH2RMKM/SfZ7NrFoej4J
In the case of WinRT, you can use PDFViewCtrl.GetCanvas() and stick the widget on that canvas using the above approach to find the coordinates.