1. A digital document management system that manages document information created in a digital form, comprising: a partial identification information generation section that divides the document information into a plurality of parts and generates partial identification information based on the respective parts of the document information and that represents, in an identifiable manner, respective parts of the document information, and that executes; assigning a random number to respective parts of document information to be newly registered, applying a hash function to the random numbers assigned to respective parts of the document information, to generate hash information, generating partial identification information composed of position information indicating to which part of the document information the generated hash information corresponds and the hash information, and generating, if any correction instruction has been given to the respective parts of the document information, the hash information for a part of the document information that has been corrected according to the correction instruction and correcting the partial identification information based on the hash information using a new random number to generate new partial identification information; a partial correction information generation section that generates partial correction information which is information representing a correction history of a corrected part if any correction instruction has been given to the respective parts of the document information; a management section that executes: storing the document information to be newly registered and partial identification information generated by the partial identification information generation section in association with each other, and storing, if any correction instruction has been given to the respective parts of the document information, document information corrected from the previous version, newly generated partial identification information, and partial correction information in an associated manner; a registration document verification section that verifies, if there has been issued a request of verifying the validity of the document information, the validity of the document information by specifying a corrected part in the document information by using the partial correction information stored in association with the document information by the management section, comparing the partial identification information associated with the document information and partial identification information associated with the document information of the previous version before correction, and confirming that the correction has been made to the specified part and the part of the document information other than the specified part has not been corrected.