The document contains the user's data. For illustration, after working on a text processor, the user may wish for to save the file. Such an action builds a document and this document must reside someplace. In a similar way, to use an existing file, the user should position it, open it, and make it accessible to the application. These 2 jobs and many others are handled behind the scenes as a document. To generate the document section of this architecture, you should derive an object from the CDocument class.