I'm using Opera Browser and when I double click on a .pdf it will be shown inside Opera. No Acrobat Reader installation required. 
How can I use Opera Browser in the viewer pane?
Currently only Opera icon will be shown:
Thanks a lot
Opera doesn't provide any way to embed it into another window, as far as I'm aware.
No browser since IE has provided that functionality, as much as it would be useful (and should be part of the OS!) to have reusable HTML and web components.