1. An information processing apparatus for managing document images, comprising: a designation unit configured to designate an area from which index information is to be extracted, in inputted document image data; a setting unit configured to set an index item for the area designated by said designation unit; a generation unit configured to generate index extraction information where information specifying the designated area is linked with information indicating the index item set by said setting unit; and a combining unit configured to combine the index extraction information generated by said generation unit with said document image data.