iTextSharp bookmarks

I have an app that creates a PDF document using iTextSharp. After the document has been created I need to add bookmarks to it. I don't want to add any extra pages I just want bookmarks that will take to user to a certain page when they click on it. I have found lots of examples online but I haven't been able to get it working. Just to get me started could someone tell me how to add a bookmark structure to an existing PDF document without adding any extra pages. eg the following structure for a 5 page document:

Code:

---

|---Page 1
|      |
|      --- Page 2
|      |
|      --- Page 3
|
|---Page 4
|      |
      --- Page 5

---

Thanks in advance