Roy Davis’s Blog

Adobe Reader comes with Adobe’s PDF preview handler but the installer has a mistake which means the preview handler does not work on 64-bit systems.  The problem can be fixed via a simple registry change.

Here’s a manual fix: 1. Open RegEdit and go to: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID\{DC6EFB56-9CFA-464D-8880-44885D7DC193} – there should be an existing AppID value, incorrectly set to {6d2b5079-2f0b-48dd-ab7f-97cec514d30b} – change the AppID value to {534A1E02-D58F-44f0-B58B-36CBED287C7C}

I found this info on http://www.ditii.com/2009/09/11/fix-for-adobe-pdf-preview-handler-bug-in-64-bit-windows/