Likewise the movie formats avi, wmv etc the Adobe PDF files can also made to either show or disable the thumbnail preview in the explorer.

While the PDF thumbnail preview is enabled for most of the users by default, but if it is not the case with you then you can make it show.

To enable or disable the preview we need to make changes in the registry HKEY_CLASSES_ROOT\AcroExch.Document.7\Shellex\{BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}

Steps:

1.    Just download this registry created called pdf-thumbnail.zip

2.    Extract the file and find two registry files called pdf-thumbnail-disable.reg and pdf-thumbnail-enable.reg

3.    Double click pdf-thumbnail-disable.reg to disable the preview while double clicking the file pdf-thumbnail-enable.reg will enable it.