I've been using  this add-in for a couple of weeks now but Foxit has been my preferred PDF reader for several months.  I find it to be very fast and functional.  At last, with the preview handler I can open PDF files directly in Outlook!

(update 3/7/2007 12:11 AM - I originally had a typo in the title with "ODF" rather than "PDF".  A rather important correction!)

Link to Foxit PDF Preview Handler