To display a mark properties window for your custom mark (when the Properties context menu item is selected, or when the PageView.ShowMarkPropertiesWindow method is called for a custom mark), you can override the GetPropertiesWindow method of your custom mark class that derives from ImGearAnnotatorMarkController or ImGearAnnotatorRectangleController. This method will need to return an instance of a class that implements IImGearMarkEditorWindow. Information on the custom mark Properties context menu item and other custom mark context menu items can be found in the Context Menu section.