Upon searching for a digital document of a document image, if information indicating a security level "vector conversion of objects is NG" is embedded in the document of interest, information of objects to be used in the search is deficient, thus disturbing satisfactory search processing. To solve this problem, a document image is read, and the read image is divided in accordance with the attributes of image regions. Designation of an image region whose image is to be vector-converted of the divided image regions is accepted, and additional information included in the designated image region is extracted. Search processing of a data file corresponding to the document image is controlled in accordance with the presence/absence of the additional information or the interpretation result of the additional information.