Maybe you already were infected by this malware, but did not have the Adobe file installed for it yet to wake up the malcode for it to become active. It is a detection for exploit code, in order for the exploit to work it has to be able to exploit a vulnerability in your PDF reader. First trick is that it tries to have you open it, and apparently you did.
Maybe you have to wait for essexboy here to have a look. It could well that some adware brought this malware along. Well wait for him to have a look. With 6 on VT alerting this it sure is no FP,
polonus