If you’re like me and have finally made the move to a 64bit version of Windows, be it Vista or Windows 7, you may have come across an annoying glitch related to PDF previews within Outlook 2007. Instead of displaying the PDF correctly you receive an error similar to “This file cannot be previewed because of an error with the following previewer: PDF Preview Handler for Vista -  To open this file in its own program, double-click it.”

Adobe Acrobat and Reader both come with Adobe PDF preview handlers for Outlook but the installer has a mistake which means the preview handler does not work on 64-bit systems. It turns out the problem can be fixed via a simple registry change.

All that needs to be done to correctly preview PDF docs in Outlook 2007 64bit is to first download the latest Adobe Reader, then add the following key to your registry;

[HKEY_LOCAL_MACHINESOFTWAREWow6432NodeClassesCLSID{DC6EFB56-9CFA-464D-8880-44885D7DC193}]

"AppID"="{534A1E02-D58F-44f0-B58B-36CBED287C7C}"

The fix should only be applied to 64-bit versions of Windows that have Adobe Reader installed. Don’t apply the fix to 32-bit versions of Windows.  To install make it easier to configure, download the adobe_pdf_x64_fix, unzip then double-click the adobe_pdf_x64_fix.reg file and follow the prompts.

thanks to http://www.pretentiousname.com/adobe_pdf_x64_fix/index.html for this workaround..