Traverse / Edit Document

So far, most of the tutorials/sample deal with creating a new document from scratch with document builder or searching through a document with its section, paragraph, nodes objects. Is there an example that edit an existing document by parsing through its content and insert/remove certain nodes base on some condition? What's a good way to transverse through the document with the document builder? I know there are all those MoveTo functions but they require you to know ahead of time where you want to go.

If you give me a more concrete scenario what you are trying to do, we will come up with suggestions. It will also help to create more samples and improve documentation.