Adobe Reader, the ubiquitous PDF reader, has become increasingly targeted by malware. Just check out the Adobe Security bulletins and advisories page for the long list of security updates Adobe has released recently.
There are a few things you can do to reduce your risk of falling prey to a malicious PDF. These steps will only take you a few minutes.
First, set Adobe Reader to update automatically. Software is supposed to simplify life, right? Let it worry about keeping itself updated so you don't have to. Adobe recommends automatic installation to ensure that you always have the latest version.