I had the same problem of opening pdf file in ie 9. The acrobat installed on my computer is Acrobat Pro XI on Win 7. I did many of the things suggested here as well as on other websites. I even upgraded to ie 10 but with no result. Then I noticed that there is one addon in ie called "wxdownloader class". I uninstalled it through add/remove on control panel and immediately I was able to open pdf pages. Good Luck to you also!