A printing apparatus and method for processing data in the printing apparatus includes estimating a printing time by adding an intermediate data generation time and a rendering time, determining whether the estimated printing time of each page keeps up with a timing at which an image needs to be formed on a conveyed sheet for each page. If it is determined that the estimated printing time does not keep up with the timing at which the image needs to be formed, further determining whether an idle time is present by comparing the intermediate data generation time and the rendering time. If it is discriminated that the idle time is present, the changing an optimization level for determining whether to perform processing on a particular object in the document image data during rendering, or to perform the processing during intermediate data generation.