A data conversion system comprising: a POS terminal device configured to transmit print data including character data and control commands; a printer configured to: • receive and transmit the print data sent by the POS terminal device , • acquire customer identification information, • add the acquired customer identification information to the print data, and • transmit the print data to a server ; and the server configured to: • receive the transmitted print data from the printer , • store the received print data in a storage unit of the server ; • extract print objects identifying print content to be printed from the print data, • reference a printing pattern stored as a predefined rule in the storage unit , the printing pattern identifying rules for inferring attribute information describing the content of print objects contained in the print data, from the order or layout of print objects, • infer attribute information of the print objects contained in the print data based on the predefined rule, • generate a tagged file having the inferred attribute information added to the extracted print objects, • generate an image file of an output image of a printout from the printer based on the print data, and • store the tagged file and the image file together with print data identification information and the customer identification information. a POS terminal device configured to transmit print data including character data and control commands; a printer configured to: • receive and transmit the print data sent by the POS terminal device , • acquire customer identification information, • add the acquired customer identification information to the print data, and • transmit the print data to a server ; and • receive and transmit the print data sent by the POS terminal device , • acquire customer identification information, • add the acquired customer identification information to the print data, and • transmit the print data to a server ; and the server configured to: • receive the transmitted print data from the printer , • store the received print data in a storage unit of the server ; • extract print objects identifying print content to be printed from the print data, • reference a printing pattern stored as a predefined rule in the storage unit , the printing pattern identifying rules for inferring attribute information describing the content of print objects contained in the print data, from the order or layout of print objects, • infer attribute information of the print objects contained in the print data based on the predefined rule, • generate a tagged file having the inferred attribute information added to the extracted print objects, • generate an image file of an output image of a printout from the printer based on the print data, and • store the tagged file and the image file together with print data identification information and the customer identification information. • receive the transmitted print data from the printer , • store the received print data in a storage unit of the server ; • extract print objects identifying print content to be printed from the print data, • reference a printing pattern stored as a predefined rule in the storage unit , the printing pattern identifying rules for inferring attribute information describing the content of print objects contained in the print data, from the order or layout of print objects, • infer attribute information of the print objects contained in the print data based on the predefined rule, • generate a tagged file having the inferred attribute information added to the extracted print objects, • generate an image file of an output image of a printout from the printer based on the print data, and • store the tagged file and the image file together with print data identification information and the customer identification information. <EOS>