A document processing technique using a computer having an application program for creating application data and a layout program for performing layout processing of document data is provided. A document processing method according to the present invention includes a conversion step of converting application data created by the application program into document data processible by the layout program, in response to an instruction from the application program, and a control step of controlling to open the document data obtained in conversion processing, by the layout program in response to conversion processing in the conversion step.