Unfortunately, even after several YEARS, Adobe has yet to fix a very simple issue with their Acrobat Reader plug-in for Microsoft Office. If you're like me and use Outlook 2007 on a 64-bit system, this is for you. I recently discovered the fix, and wanted to sum it up here for you. The total write-up is available here. It's simple enough, simply open up your Registry Editor and point it to:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID\{DC6EFB56-9CFA-464D-8880-44885D7DC193}

In there you'll see a value for AppID. Change that to {534A1E02-D58F-44f0-B58B-36CBED287C7C} and you're all set!