1. An image forming apparatus, comprising: an image rotation processor configured to: obtain form image data; identify a direction of an upper edge of a document image on a first page; rotate the form image such that the direction of the upper edge of the document image on the first page matches a direction of an upper edge of a form image if the direction of the upper edge of the document image on the first page differs from the direction of the upper edge of the form image based on the form image data; and rotate a document image on each page of the second page and the subsequent pages such that the direction of the upper edge of the document image on the first page matches a direction of an upper edges of the document image on each page of the second page and the subsequent pages if the direction of the upper edge of document image on each page of the second page and the subsequent pages differs from the direction of the upper edge of the document image on the first page; and an image combination unit configured to combine the form image processed by the image rotation processor with the document image on each page.