Vulnerability reported in Foxit PDF plugin for Firefox - how to mitigate it
Also, since Adobe released Reader X, with its security-oriented sandbox, crooks and researchers alike have found Adobe's PDF nut much harder to crack.
You can therefore expect other vendors of PDF software to start feeling some of the heat that would probably have been aimed entirely at Adobe in years gone by.
Here's an example: Italian security researcher Andrea Micalizzi has recently sought, and found, a possibly-exploitable vulnerability in the latest Foxit PDF plugin for Firefox.
http://nakedsecurity.sophos.com/2013/01/11/vulnerability-in-foxit-pdf-plugin-for-firefox/