A document processing apparatus reads document data and carries out a preflight check. In the preflight check, the content of the document is interpreted page by page to determine resources that are needed for output. Then, it is determined for each page whether the resources needed for output are available in a printing system. If a resource that is not available is needed, a warning is issued for the page. If the resources are available, intermediate data for a printed output is generated for the page. Then, a result of the preflight check is output.