An image forming apparatus includes a reception unit which receives an electronic document, a generation unit which generates a display list containing edge information indicating the outline of an object contained in the received electronic document, fill information for controlling whether to fill in the inside of the outline of the object, and control information for controlling image formation of each page that forms the electronic document, an edge position extraction unit which obtains the intersections of the object and the line based on the edge information, and extracts the positions of the edges of the object on the line, and a setting unit which sets, based on the data amount of extracted edges and the data amount of edges in the page that is predicted by analyzing the control information, a threshold for controlling extraction of the edges to fall within a predetermined data amount.