pdf is not exporting

function Export() {
       var grid = $("#grid").data("kendoGrid");
       var dataSource = (grid != null) ? grid.dataSource : null;
       var filters = (grid != null) ? dataSource.filter() : null;
       var allData = dataSource.data();
       var query = new kendo.data.Query(allData);
       var data = query.filter(filters).data;
       var dataJSON = JSON.stringify(data);

$.ajax({
           url: '@Url.Action("Print_PDF", "controlllername")',
           //dataType: 'json',
           data: {
               gridData: dataJSON
           },
           ContentType:'application/json; charset=utf-8',
           //traditional: true,
           type: 'POST',
           success: function (result) {
               alert("ok: "+ result);
           },
           error: function (result) {
               alert('Oh no: '+ result.responseText);
           }

       });

public ActionResult Print_PDF_EX(string gridData)
{
//write data to pdf code here
return  File(stream, "application/pdf", fileName);
}