There are security flaws within Adobe Reader and Acrobat and the Adobe Flash Player which are getting actively exploited on the net currently. The company has published a security advisory where it announces that they are currently investigating the problem and plan an update for the 30th of July.
Avira antivirus solutions already detect the malicious PDF files as EXP/Pidief.TH and the dropped malware by those documents as TR/Drop.Wmach and TR/Spy.WMach, respectively. Anyhow it is a good idea to take additional security measures until Adobe provides an update.
Adobe recommends to delete or rename the file authplay.dll that ships with the Reader and with Acrobat. Also, enabling Data Execution Prevention (DEP) and activating the User Access Control (UAC) in Windows Vista shall mitigate the risk according to Adobe.
Another solution would be using a different PDF reader and disabling Adobe PDF and Flash within the web browser via its add-ons-manager. The NoScript extension for Firefox also helps preventing Flash applications to run in the browser; it is possible that drive-by-downloads via malicious Flash applications embedded in web sites turn up soon.