This invention generates a digital document by applying character recognition to character images in a document image, and rendering the character recognition result on the document image in a transparent color. This digital document allows to specify a part corresponding to a search keyword on the document image upon conducting a search. When this digital document is generated, it includes a description required to use glyph data (font data) of a simple character shape commonly to a plurality of character types as font data used upon rendering the character recognition result. Therefore, even when the digital document needs to save font data, an increase in file size can be minimized. Also, by rendering using a simple character shape, the data size of the font data itself can be reduced.