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(3) has not been called before.
In such cases the BoundingBox would be left unset unless you set
it explicitly with this function.