Description
bool 
fdf_set_ap ( resource fdf_document, string field_name, int face, string filename, int page_number)
   The fdf_set_ap() function sets the
   appearance of a field (i.e. the value of the /AP key).
   The possible values of face
   are FDFNormalAP, FDFRolloverAP 
   and FDFDownAP.