A user wants to select a number of customer documents and then run a macro which composes a standard document for each of the selected customer documents.
Have the macro's Operation set to Compose new documents when run.
In the Formula add a statement:
FIELD Form := name_of_the_standard_document_form;
If you only need to print out forms with existing data, this is even simpler. Highlight the documents in the view and then select File, Print, Form Override.