1. An image processing apparatus comprising: an acquiring unit that acquires image data representing a document image that includes characters; an extracting unit that extracts, from the document image represented by the image data, a character that has undergone a modification for distinguishing from another character; a processing unit that processes the image data by reducing a density of the character other than the extracted character below a density indicated by the acquired image data; and an output unit that outputs the image data processed by the processing unit to an image forming apparatus.