How to draw on pdf displayed in web browser control in wpf

Question

I am working on a project where i need to enable user to draw shapes on PDF file at runtime.

I am able to draw shapes on canvas using mouse events.

To open PDF file in my wpf application i have used  web browser control and over it i have put a transparent canvas but since according to microsoft documentation, browser control is always on the top, mouse events of canvas are not firing.

 

Please suggest me the right direction to go.

 

Thanks in advance.