The XML Adapter operations (Parse/Generate) always need either an XML document instance, DTD or XML Schema so that it can determine the structure of potential documents and create the output mappings. If you do not have a DTD for the xml messages you are integrating, you will need to create one before you can use the adapter operations.
It is usually good practice to define a DTD or Schema so that you have an interface contract, but I have my own integrations where the other application just creates the messages in an ad hoc manner, so I had to define a schema myself so I could use the adapter operations.
You are correct, there is no license key required for the XML adapter.
Steve
#webMethods#Integration-Server-and-ESB