The print_compositor service should composite multiple raw pictures from different frames into a complete one, then converts it into a print document format, either PDF or XPS. This all happens within an isolated sandboxed process.

While the compositor creates single-page PDF objects it can optionally collect those into a multi-page PDF or XPS document object. Otherwise a multi-page PDF document is made by sending an extra multi-page metafile which contains repeats of each of the previously processed pages all in one larger message.

Message flow when interacting with the print document compositor is as follows: