void cpdf_add_annotation (int pdf document, double llx, double lly, double urx, double ury, string title, string content [, int
mode])
The cpdf_add_annotation() adds a note with the lower left corner at (llx, lly) and the upper right corner at (urx, ury).
The optional parameter mode determines the unit length. If it's 0 or omitted the default unit as specified for the page is used. Otherwise the coordinates are measured in postscript points disregarding the current unit.