1. An image forming apparatus comprising: an interface which receives a job including a plurality of documents and a page number of a designated page to be printed, wherein the page number of the designated page to be printed is not designated by a document page number; a memory storing instructions; and one or more processors which execute the instructions to: serially renumber each page of each document of the plurality of documents, based at least on a number of pages in each document, so that each page in the job has a unique page number; and specify, based on the serially renumbered pages of the job and the received page number of the designated page to be printed, a serially renumbered page to be printed in the job.