Abstract: Systems and methods for assembling parts of a multi-part document. An example method comprises: assigning a plurality of image processing tasks to a plurality of worker processes; defining input parameters for each task of the plurality of tasks, the input parameters comprising a part of an original document and a structure definition of the part, the structure definition including a reference to a element requiring time-consuming processing (e.g., graphical element) comprised by the part of the original document; and outputting, into a file representing the original document, a plurality of images produced by the plurality of worker processes based on elements requiring time-consuming processing (e.g., graphical elements) defined by the input parameters.