Document processing apparatus storing and modifying data using effect data

1. Field of the Invention A document processing apparatus simplifies a user's manipulations for selecting a layout or inserting a part into a selected layout, and enables a user to increase the number of parts the user can choose with a simple manipulation and without an increase in storage capacity for parts. A layout/parts list display control unit defines a layout area and a parts list area in a screen on a display unit on the basis of layout data and part data, displays one layout or a plurality of layouts in the layout area, and displays a list of parts to be inserted into the layouts in the parts list area. A part insertion unit, in response to selection of one part from the list of parts, inserts the part into associated fields in all the layouts displayed in the layout area. An effect data memory unit stores effect data used to modify part data and a modification unit modifies part data in accordance with effect data.