Saving canvas as pdf

Question

I have tried a script which save canvas as png but I want to save it as pdf. I tried many scripts but not working for me. The script od saving png:

    // Initializing
window.onload = function(){
  var dwn = document.getElementById('btndownload'),
      canvas = document.getElementById('canvas'),
      context = canvas.getContext('2d');

  // Drawing a circle
  var centerX = canvas.width / 2;
  var centerY = canvas.height / 2;
  var radius = 70;
  context.beginPath();
  context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
  context.fillStyle = 'rgba(0,200,0, .7)';
  context.fill();
  context.lineWidth = 2;
  context.strokeStyle = 'black';
  context.stroke();
  
  // Drawing a rect
  context.beginPath();
  context.rect(15, 50, 100, 100);
  context.fillStyle = 'rgba(255,255,0, .7)';
  context.fill();
  context.lineWidth = 2;
  context.strokeStyle = 'black';
  context.stroke();

  // Event handler for download
  dwn.onclick = function(){
    download(canvas, 'myimage.png');
  }

}

live demo of it