1. An image forming apparatus comprising: a read unit configured to read an image of a source document and obtain image data; an electronic document production unit configured to produce electronic document data for allowing a display apparatus to display said image data thereon, based on said image data; an extraction unit configured to extract from said image data an additionally-written region including an additional portion, and configured to identify the additional portion and distinguish the additional portion by associating the additional portion with a unique identifier corresponding to a plurality of different types or attributes; an annotation data production unit configured to produce annotation data based on said additionally-written region, and configured to inspect the unique identifier corresponding to the plurality of types or attributes, and based on the unique identifier, execute different processing for each produced annotation data having a corresponding unique identifier; and; a setting unit configured to calculate a position for allowing said display apparatus to display said annotation data on said electronic document data, based on a position of said additionally-written region on said image data, and setting the calculated position for said annotation data.