Resource files can be shared and referenced by multiple models or copied to and embedded in a single model. Any modifications that you make to a shared resource are available to all models using the resource, while modifications to an embedded resource are available only to the model in which it is embedded. Embedded resource files are saved as part of their model and not as a separate file.
You should never modify the original extensions shipped with PowerDesigner. To create a copy of the file to modify, open the List of Extensions, click the New tool, specify a name for the new file, and then select the .xem that you want to modify in the Copy from field.
The File Name field displays the location of the resource file you are modifying is defined. This field is empty if the resource file is embedded.