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.