The plug-in modifier must provide a mechanism to actually modify or deform the object. When a modifier needs to be applied to an object, 3ds Max calls the Modifier::ModifyObject() method. This method is responsible for deforming the object and updating the validity interval of the object to reflect the validity interval of the modifier.
The simple modifier base class SimpleMod provides a default implementation of Modifier::ModifyObject() and instead requires that the method SimpleMod::GetDeformer() is overridden. For more information see the topic Using a Deformer.