4. The non-transitory computer readable storage medium of claim 2 , wherein, when conducting the insertion of the document and when the Fixed Page is not designated, the third function further includes: 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, and wherein, when conducting the overwriting of the document and when the Fixed Page is not designated, the third function further includes: 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, and wherein, when conducting the insertion of the document and when the Fixed Page is designated, the third function further includes: 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 wherein, 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.
2. The non-transitory computer readable storage medium of claim 1 , wherein the program causes the image forming apparatus to perform: a first function that includes: 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 designating a single first relationship or plural first relationships between the first elements created, when conducting a creation, an insertion or an overwriting of a document, a second function that includes: 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 that includes: 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.