A document providing computer creates a JDF file and a PDF file, and associates them by embedding a path to the PDF file in the JDF file (S000). When guaranteeing this combination, a hash calculation is performed for the JDF file, and the obtained hash value is embedded in the PDF file. The PDF file, except for the embedded hash value, is then encrypted using as a key the obtained hash value (S003). With a computer for printing the document, the PDF file is decrypted using the embedded hash value, and the hash value is re-calculated and compared with the embedded hash value, thus validating the correctness of the combination.