This is a "Unit of Work" object (see "Unit of Work" pattern by Martin Fowler,
http://www.martinfowler.com/eaaCatalog/unitOfWork.html
: the unit of work "maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems".
In the current design, this interface allows a use case to generate documents, while ensuring that only one instance of a document is created.