A region division portion extracts an “object”, an “anchor expression accompanying the object” and a “text including the anchor expression” from image data based on a paper document and an electronic document. A link processing portion generates link information that associates, in two ways, the “object”, the “anchor expression included in the text” or the “text including the anchor expression” with each other. Then, a format conversion portion converts the link information into electronic document data including two-way link information. When this electronic document data is displayed by an application and one of the “object” and the “anchor expression included in the text” is selected, the other can be displayed according to the link information.