A Rational RequisitePro document type defines descriptive and operational characteristics associated with a requirements document. The document type serves as a template for each requirements document you create of that type.
The document type defines the document’s file extension, such as ".prd"; all documents of the same document type share the same file extension. The document type identifies a default requirement type; each new requirement you create in the document is based on the default requirement type unless you indicate otherwise. The document type also identifies an outline (or template) for the document, which controls such characteristics as page layout, default text, and paragraph styles.