itextsharp trimming pdf document's pages

I have a pdf document that has form fields that I'm filling out programatically with c#. Depending on three conditions, I need to trim (delete) some of the pages from that document.

Is that possible to do?

for condition 1: I need to keep pages 1-4 but delete pages 5 and 6

for condition 2: I need to keep pages 1-4 but delete 5 and keep 6

for condition 3: I need to keep pages 1-5 but delete 6