It could also be that the session id is what is being stored as a cookie (this is very common). By deleting your cookies, you will get a brand new session the next time you hit a page. If you are storing your forms in session, I suspect that this is the cause of you problem.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com