18. A computer readable medium storing a computer executable program for creating document data that include a digital signature, the program comprising program code for causing a computer to perform the steps of: calculating a characteristic value for every object included in the document data based on the document data; attaching the characteristic value, serving as the digital signature, to every object included in the document data; and designating a specific object included in the document data; wherein a value, which is different from the characteristic value of the specific object, calculated in the calculating step, is selectively attached to the specific object, designated in the designating step, as the digital signature to be included in the document data.
18. A computer readable medium storing a computer executable program for creating document data that include a digital signature, the program comprising program code for causing a computer to perform the steps of: calculating a characteristic value for every object included in the document data based on the document data; attaching the characteristic value, serving as the digital signature, to every object included in the document data; and designating a specific object included in the document data; wherein a value, which is different from the characteristic value of the specific object, calculated in the calculating step, is selectively attached to the specific object, designated in the designating step, as the digital signature to be included in the document data. 21. The computer readable medium of claim 18 , wherein the document data are created, based on a XPS; and wherein information for instructing a printing apparatus to implement a printing operation in a predetermined print mode, in which an object, the characteristic value of which is valid, should be printed, while another object, the characteristic value of which is invalid, should not be printed, are attached to the document data.