Hi Amith,
I think you will have to copy them to a location that can be referenced via a http/https url. Then using app.launchURL will open the document in whatever application is registered on the client machine to handle that extension type. We have forms containing links to documents uploaded by the user and stored in Sharepoint. When the user clicks the link on the PDF form a webservice is called to copy the Sharepoint file to the webserver and returns the url of the file, which we then pass into app.launchURL().
Regards
Bruce