No program will display a pdf popup in Explorer, merely on hover, they all need you to first activate the file - also Quick Tool (right-click). There are a couple of viewers that will display them all, pdf pics text rtf, but not in Explorer. Wouldn't it be enough for you to have page 1 as a thumbnail (view: "large icons")?:
I use Nitro Pro 6 OCR, but almost any good pdf editor will give you this feature in Explorer. For pre-viewing photos and text files, I use Quizo QTTabbar, but I cannot make a screenshot of it, to show.