app.post('/', function(req, res) {
 console.log("post request detected");

  let pdfParser = new PDFParser(this, 1);

  pdfParser.on("pdfParser_dataError", function(errData) {
    console.error(errData.parserError)
  });
  pdfParser.on("pdfParser_dataReady", function(pdfData) {
    fs.writeFile("./public/data.json", JSON.stringify(pdfData));
  });
  //so here I have to pass the path of the file, now i wrote it manually to test
  pdfParser.loadPDF("C:\Users\Lenovo\Downloads\schedule.pdf");
});

<input type="file" id="file"/>
<input class="btn btn-primary" ng-click="fileSubmit()"  type="submit" value="submit"/>

$scope.fileSubmit = function() {
  //here it work when i write it manually :)
  $http.post('/', "C:\Users\Lenovo\Downloads\Personal Schedule.pdf");
};