unfortunately Acrobat 9 is no longer supported by Adobe.
So why wouldn't Adobe support it's own products? I know the API is kind of weak - i.e. the objects and their associated properties are small in number BUT my thought is if there is a way to create the nested bookmarks using a drag-and-drop GUI method, why wouldn't there also be a method / menu executable item / object property that an open sourer like myself can manipulate?
Another question I could get answered is: Is there any way to create nested bookmarks OTHER than using drag-and-drop from within Acrobat?