You may have read Bojan's excellent diary earlier this month where he looks at a couple of new PDF exploits with zero AV coverage. The low coverage was likely to be caused by a funky method of confusing the AV engine when its parsing the Javascript contained within the PDF.

Well,  Didier Steven's has written an analysis of those files and it an excellent read. Go take a look at his blog entry on Shoulder Surfing a Malicious PDF Author. 

Steve Hall