UIManagedDocument is a concrete subclass of UIDocument that integrates with Core Data. When you initialize a managed document, you specify the URL for the document location. The document object then creates a Core Data stack to use to access the document’s persistent store using a managed object model from the application’s main bundle.
The persistent store coordinator is set up automatically for you and you can configure it using it's persistentStoreOptions property. -you can use it as a data container, not just for documents. -you can listen to state and store content changes, which makes iCloud syncing easier
Read Apples documentation or an article by Erica Sadun. There is also a great demo video from Stanford Universities Paul Hegarty - check the Core Data demo on iTunes U.
