In a data processing apparatus which forms a file having a plurality of pages on the basis of image data obtained by sequentially reading images on a plurality of originals, forms a file having the attribute information and end information representing the end of the file for each page, and transmits the file, when file creation processing is interrupted midway during file creation, the end information of the file is added at the interrupt time, thereby transmitting a normal file. In addition, data to be formed into one file is divided into a plurality of blocks in units of pages, and a plurality of files each having end information are sequentially transmitted. At this time, information for allowing the receiving side to convert the divided files into one file is transmitted. Furthermore, a plurality of data stored in a memory are appropriately selected, one file having a plurality of pages is formed on the basis of the selected data, and a file having the attribute information and file end information for each page is formed and transmitted.