Preview in Apple Mac OS X 10.5.2 uses 40-bit RC4 when saving a PDF file with encryption, which makes it easier for attackers to decrypt the file via brute force methods.
https://exchange.xforce.ibmcloud.com/vulnerabilities/41276
http://www.vupen.com/english/advisories/2008/0924/references
http://www.us-cert.gov/cas/techalerts/TA08-079A.html
http://www.securitytracker.com/id?1019665
http://www.securityfocus.com/bid/28386
http://www.securityfocus.com/bid/28304
http://secunia.com/advisories/29420
http://lists.apple.com/archives/security-announce/2008/Mar/msg00001.html