A. To enable the preview of PDF files in 64-bit OSs, do the following:

  1. Start the Registry Editor (Start, Run, Regedit.exe).
  2. Move to HKLM\SOFTWARE\Wow6432Node\Classes\CLSID\\{DC6EFB56-9CFA-464D-8880-44885D7DC193\}.
  3. Change the AppID value to \{534A1E02-D58F-44f0-B58B-36CBED287C7C\}.
  4. Reboot.
Related Reading:

Check out hundreds more useful Q&As like this in John Savill's FAQ for Windows. Also, watch instructional videos made by John at ITTV.net.