It is the reference to PDF file formats that has frightened off correspondents. PDF is not an Office format, so programming Office products to search PDF is difficult and will be affected by how the PDF files were created and what software you have.
In practice it requires a PDF compatible product that is programmable from VBA. Essentially that means you will need Adobe Acrobat and not merely Adobe Reader.
If you had Word 2013, that offers another avenue as that can open PDF format, but your post does not acknowledge the presence of either.
If you have Acrobat then the code at
http://www.myengineeringworld.net/20...rough-vba.html should help with the search and that (while aimed at Excel) should be adaptable to Outlook.
If you have Acrobat report back and we'll come up with a function that will work from a rule.