ApplicationControl has a ApplicationType property that allows developers to specify how many DocumentControls will be used in a given application. If this property is set to ApplicationType.SingleDocument, non-native file loaders and the Presenter materials will also be available. However using an additional DocumentControls will throw 'InvalidOperationException' exceptions when accessing the Documents of the additional DocumentControls.`
i.e. when you want to work with any type of files in a view control application, you must set ApplicationType.SingleDocument.