The AddViewport method allows adding a Viewport object to the Viewports array of the page specified.
System.Integer AddViewport(System.Integer PageNumber, IViewport viewport)
PageNumber
Number of the page where the viewport will be added Page indexes start at 1.
viewport
Viewport object to add.
True if the Viewport was added successfully, False otherwise.
Please check this link.
Member of CDIntfEx.IDIDocument.