convert pdf to base64 javascript

// Check for the File API support.
if (window.File && window.FileReader && window.FileList && window.Blob) {
  document.getElementById('files').addEventListener('change', handleFileSelect, false);
} else {
  alert('The File APIs are not fully supported in this browser.');
}

function handleFileSelect(evt) {
  var f = evt.target.files[0]; // FileList object
  var reader = new FileReader();
  // Closure to capture the file information.
  reader.onload = (function(theFile) {
    return function(e) {
      var binaryData = e.target.result;
      //Converting Binary Data to base 64
      var base64String = window.btoa(binaryData);
      //showing file converted to base64
      document.getElementById('base64').value = base64String;
      alert('File converted to base64 successfuly!\nCheck in Textarea');
    };
  })(f);
  // Read in the image file as a data URL.
  reader.readAsBinaryString(f);
}