The Select Extensions dialog allows you to attach extensions to your model at creation time. Extensions may contain additional types of objects or extensions to standard objects, along with additional generation targets and other extensions to PowerDesigner's standard capabilities.
By default, PowerDesigner creates a link in the model to the specified file. To copy the contents of the extension file and save it in your model file, click the Embed Resource in Model button in the toolbar. Embedding a file in this way enables you to make changes specific to your model without affecting any other models that reference the shared resource.