An image processing apparatus which has a reading unit configured to read an image of a document and generate image data acquires a process definition file which defines a content of reading processing to be executed and a content of transmission processing for transmitting the generated image data, causes the reading unit to execute the reading processing to generate image data according to a definition described in the acquired process definition file, requests an external apparatus to transmit the generated image data according to the definition described in the acquired process definition file, adds, to the acquired process definition file, a description for causing the external apparatus to execute processing for notifying a result of the transmission by the external apparatus, and makes the request by transmitting, to the external apparatus, the generated image data and the process definition file to which the description is added.