For fdf_save you need to provide the complete path, such as :fdf_save($outfdf,"c:/inetpub/wwwroot/temp_sites/fdf/outtest.fdf"); and not only outtest.fdf.
For fdf_save you need to provide the complete path, such as :fdf_save($outfdf,"c:/inetpub/wwwroot/temp_sites/fdf/outtest.fdf"); and not only outtest.fdf.