This would have a lot of possibilities....

True, but that would also introduce too many possibilities of error: how do you handle finishing if both documents have conflicting settings? How do you tell the second document which data to use? (Presumably, you'd only want it to use the record currently being processed in the first document... but then again, maybe not).

This type of application, is best handled using the many PDF and/or metadata tasks available in the Workflow tool and which allow you to mix and match documents.