Sets certain information fields of the document. This fields will be shown as a comment in the header of the PostScript file. The values which can be set are Keywords, Subject, Title, Creator, Author, BoundingBox, Orientation. Be aware that some of them has a meaning to PostScript viewers.
The BoundingBox is usually set to the value given to the first page. This only works if ps_findfont() has not been called before. In such cases the BoundingBox would be left unset unless you set it explicitly with this function.