I need to generate pdf for few html summary pages. And the html summary page will be available only for authenticated users.
How can we generate pdf for authenticated urls ?

It depends on the server side session mechanism of you web application. You need to propagate the session ID correctly with the URL passed to PD4ML.

For the regular J2EE application a solution is to add the jsessionid parameter to URLs:

http://your.server.net/webapp/sourcepage.jsp;jsessionid=8764587625?param1=value1&param2=value2

How will this work with .Net MVC. need it to render an MVC action that is based on an authentication requirement.

As a rule a session ID is propagated via cookies or as an URL parameter. Just check how it is in your case and invoke pd4ml.setCookie() before render() call or add the session ID to the URL string:

http://myserver.com/(tsdfg2usdfgvrj3vxgvg)/start.aspx

(the actual sessionID-enabled URL syntax may vary)