Safari in WebKit in Mac OS X 10.4 to 10.4.2 directly accesses URLs within PDF files without the normal security checks, which allows remote attackers to execute arbitrary code via links in a PDF file.
http://www.us-cert.gov/cas/techalerts/TA05-229A.html
http://www.kb.cert.org/vuls/id/420316
http://lists.apple.com/archives/security-announce/2005/Aug/msg00000.html
http://lists.apple.com/archives/security-announce/2005//Aug/msg00001.html