Abstract: In a document processing method using a multiwindow including a display device having a display screen on which a plurality of windows are established, a virtual screen memory in which a plurality of virtual screens each corresponding to programs are generated to output results of data processing by programs, a memory unit for storing therein a window control table defining corresponding relationships between the virtual screens and the windows, and a control device for referencing the window control table and for outputting contents of each virtual screen in a window associated with the virtual screen on the display screen, copy source attribute data including an identifier of a second window established in the display screen and data defining a second partial region in the second window is memorized in correspondence with a first partial region on the vertical screen so that, in response to a command inputted by an operator while painting to the first partial region displayed in the first window, the displa