How can I get the reference of PDF file opened in Internet Explorer using c#?

I can get the browser reference through a BHO. I can able to get normal web page document but unable

to get the reference of PDF file which is opened on browser. How can I get, when I googled I found

that
Acrobat.AcroAVDoc avDoc = webBrowser.Document as Acrobat.AcroAVDoc;avDoc.GetAVPageView

();avDoc.GetPDDoc();

How can I get the refernce of PDF file which is getting loaded on Internet explorer when I try to open

a PDF link...