I would like to have a thumbnail of all my .ppt/.odp/.pptx documents in my system. However, I have not seen any server/client program for the task. LibreOffice may however have something related integrated in the package. My thread/bounty about the topic also in Unix stackexchange here. Here Ubuntu’s thread about the issue.
Bernard Marcelly gave a procedure to extract thumbnail from odf here.
I have not tested for MS format…