File downloading not working in node

I am using res.download() and the file is getting downloaded as well.But the pdf which is uploaded on the server and which I am getting with res.download is different i.e the one which I am getting downloaded is blank pdf.ALso a 200 response is returned in my server i.e that the file is present. Below is my code: Controller:

$http.get('/api/knowledges').success(function(data){
        console.log("this is your data");
        console.log(data);
        $scope.knowledge=data;
    });
    $scope.download=function(fileDownload){

      function downloadFile(filePath){
        console.log("download funcion invoked");
        console.log(filePath);
        var link=document.createElement('a');
        link.href = filePath;
        //link.download = "my.pdf"
        link.click();
      }
      downloadFile('/api/knowledges/file_download/?filepath='+fileDownload.file_details.path);
    }

API:

exports.download = function(req, res) {
  var filename='BookWorm Study Material.pdf';
  res.setHeader('Content-type', 'application/pdf');
  res.download(req.query.filepath,filename);
};

via Akshay