Adobe Acrobat 9 uses more efficient encryption than previous versions, which makes it easier for attackers to guess a document's password via a brute-force attack.Referenceshttp://www.elcomsoft.com/PR/apdfpr_081126_en.pdfhttp://www.securityfocus.com/bid/32610http://blogs.adobe.com/security/2008/12/acrobat_9_and_password_encrypt.html
