I am running Outlook 2007 on Windows XP Pro. I have also got Adobe 9.1 Reader and the latest Adobe Flash installed.
If I receive a link to a PDF in Outlook and I double click it tries to open the file in IE8, even then it come back with a blank grey screen. Previous when I had Outlook 2003 it would open in Adobe. I have tried the Display PDF in Browser option ticked and unticked.