If you are running the 64-bit version of Windows 7 (or Vista), you will find that your PDF files do not preview in Windows Explorer as they do in the 32-bit versions. Instead, all you see is a message stating that This file can’t be previewed. To enable this functionality on your 64-bit operating system, follow these steps.
1. Click the Orb (Start Button).
2. Go to the Search programs and files textbox and input regedit.
3. Select regedit.exe from the results.
4. When the UAC prompt appears, click the Yes button.
5. In the left pane of the Registry Editor, go to (and select):

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Classes\CLSID\{DC6EFB56-9CFA-464D-8880-44885D7DC193}
6. In the right pane, locate AppID.
7. Change AppID value to {534A1E02-D58F-44f0-B58B-36CBED287C7C}.
8. Restart your computer for the change to take affect.
