Check if pdf is opened on web browser

As far as I remember, Joel_Geraci made a useful tuto (I can not find the link) about forcing the download of PDF files (instead of opening in the web browser), it could be a workaround.

Thanks!

Can I open the file with adobe reader?

Yes.

   if ( this.external )
   {
      // Viewing from a browser
   }
   else
   {
      // Viewing in the Acrobat application.
   }