Embodiments are provided for creating and executing a custom action in a workflow generated by an application program executing on a computer system. The application program may receive a selection of a custom action to execute in the workflow in a user interface generated by the application program. The application program may translate the custom action into a user interface button for executing the custom action in the workflow. The application program may display the button for executing the custom action in the workflow. The application program may also resolve references to external content in a shared workflow document by communicating with a workflow engine to register a callback function for receiving a location of the shared workflow document on a remote computer system. The workflow engine may send the location of the shared workflow document to the application program to enable access to the external content.