1. An image forming apparatus comprising: a document reading section that can read an image of a document; a document-type determining section that can extract, when the image includes a finishing mark or a characteristic form, the finishing mark or the characteristic form as a characteristic portion from the readout document image, and can determine, based on the extracted characteristic portion, a type of the finishing or a type of the document; a processing deciding section that decides, based on the determined type of the finishing or the determined type of the document, a type of finishing to be performed to a medium to be output or a type of image processing to be performed to an image to be output; and a processor that performs finishing of the type decided by the processing deciding section to the medium to be output or image processing of the type decided by the processing deciding section to the image to be output.