PROBLEM TO BE SOLVED: To provide a document management system which can computerize a confidential document using MFP for use in a network conference and make the confidential document left in a client unopenable after the conference, from the point that vulnerability in maintaining confidentiality is seen as a problem with increasing computerization of documents with high confidentiality (management conference document, planning paper, strategy document, etc.). SOLUTION: The system comprises the function of performing encoding processing to an image or document file stored in an HDD within the MFP, the function of transmitting the encoded file to a designated client PC, the function of generating a decoding key enabling browsing and printing of the file, and the function of transmitting the decoding key to the client PC. COPYRIGHT: (C)2007,JPO&INPIT