If the PDF is valid, you can apply watermark with the help of Rights
Management Service. You need to do following steps:- Login into LC
adminui with admin user.- Create a watermark
(http://help.adobe.com/en_US/livecycle/9.0/adminHelp/admin.htm?content=000246.html)-
Include the watermark as a part of a policy in Rights Management.- Use
the policy to apply the watermark on a PDF.Hope this helps.~ Varun