You can copy Packages, Classes, Attributes and Primitive Types between models.
The business object models can be in the same project or in different projects. To copy business objects between projects you must create a project reference between the two projects.
Procedure
In the Project Explorer, expand the business object model that contains the diagram nodes you want to copy.
Open the business object model that you want to copy the diagram nodes to.
Drag the diagram node to the Business Object where you want to add or create a new object. A menu is displayed in the new model asking what you want to do with the new object. The menu that is displayed depends on the type of business object you have copied. An example is shown below:
If the business object models are in the same project the item is copied to the new model. If the models are in different projects, a Project Reference message is displayed. Click Yes to create the project reference or No if you do not want to create the project reference. If you click Yes, the object is copied to the new model.