7. The image forming apparatus of claim 6 , wherein the processor is adapted to further perform: a first function comprising: correlating the print job with Fixed Document or Fixed Page of the XPS file; creating first elements being necessary for editing the XPS file; and, when conducting a creation, designating a single first relationship or plural first relationships between the first elements created for an insertion or an overwriting of a document, a second function comprising: shifting a number of the Fixed Document or the Fixed Page; adding all of the first elements created under the Fixed Document or the Fixed Page thereto; and registering the Fixed Document or the Fixed Page added with the first elements into a predetermined area, when conducting the insertion of the document concerned, and a third function comprising: deleting all of second elements currently set under the Fixed Document or the Fixed Page and second relationships between the second elements; adding all of the first elements created under the Fixed Document or the Fixed Page thereto; and registering the Fixed Document or the Fixed Page added with the first elements into the predetermined area, when conducting the overwriting of the document concerned.
7. The image forming apparatus of claim 6 , wherein the processor is adapted to further perform: a first function comprising: correlating the print job with Fixed Document or Fixed Page of the XPS file; creating first elements being necessary for editing the XPS file; and, when conducting a creation, designating a single first relationship or plural first relationships between the first elements created for an insertion or an overwriting of a document, a second function comprising: shifting a number of the Fixed Document or the Fixed Page; adding all of the first elements created under the Fixed Document or the Fixed Page thereto; and registering the Fixed Document or the Fixed Page added with the first elements into a predetermined area, when conducting the insertion of the document concerned, and a third function comprising: deleting all of second elements currently set under the Fixed Document or the Fixed Page and second relationships between the second elements; adding all of the first elements created under the Fixed Document or the Fixed Page thereto; and registering the Fixed Document or the Fixed Page added with the first elements into the predetermined area, when conducting the overwriting of the document concerned. 9. The image forming apparatus of claim 7 , wherein when conducting the insertion of the document and when the Fixed Page is not designated, the third function further comprises: shifting each of document numbers of Fixed Documents, assigned just after other Fixed Documents to be inserted, by a number of the other Fixed Documents; adding all of sixth elements to be set under the other Fixed Documents thereto; and registering the other Fixed Documents added with the sixth elements into the predetermined area, when conducting the overwriting of the document and when the Fixed Page is not designated, the third function further comprises: deleting all of the second elements currently set under the Fixed Document and second relationships between the second elements; adding all of the first elements created under the Fixed Document thereto; and registering the Fixed Document added with the first elements into the predetermined area, when conducting the insertion of the document and when the Fixed Page is designated, the third function further comprises: shifting each of page numbers of Fixed Pages, assigned just after other Fixed Pages to be inserted, by a number of the other Fixed Pages; adding all of seventh elements to be set under the other Fixed Pages thereto; and registering the other Fixed Pages added with the seventh elements into the predetermined area, and when conducting the overwriting of the document and when the Fixed Page is designated, the third function further includes: deleting all of the second elements currently set under the Fixed Page and the second relationships between the second elements; adding all of the first elements created under the Fixed Page thereto; and registering the Fixed Page added with the first elements into the predetermined area.