Free ESET online antivirus found PDF/exploit.Gen.Trojan

I don't know how this gotten into system, usually i run spybot, adware, malware anti-malware every now and then. btw, i ran all these which didn't detect this PDF/exploit. Can any1 tell me how i could remove this from the computer. i searched this item in google, couldn't find anyt site that showed how to remove this trojan.thanks in advance. i appreciate it a lot.
btw, as for anti-virus i have AVast.

 

Hello MHD,

If our online scanner found the threat, our free trial should be able to catch it also and remove it. http://www.eset.com/download/free_trial_download.php

Thank you,
Richard