If you are using Foxit instead of Adobe Reader to open pdf-files you can use this Preview Handler to preview PDF-attachments in Outlook 2007 and Outlook 2010 on Windows Vista or Windows 7. Even though it hasn’t been developed by Foxit (but by a Microsoft Program Manager), it does use the Foxit engine.
Download: Foxit PDF Preview Handler
When you are using Outlook 2013 on Windows 8 or Windows Server 2012 or newer, Outlook has native support for previewing pdf-files. Opening pdf-files via a double click will open it in the Reader app and can even be edited in Word 2013. Installing the Foxit PDF Preview Handler has therefor become optional.