Downloading file with http

I'm trying to download a pdf file from a link using the following code. However, I got 404 error page. The same link just work fine in browser. What would be the cause?

var http = require('http');
var options = {
  host: 'www.xxxx.xxx',
  path: '/achieved/a1.pdf'
};

callback = function(response) {
  var str = '';
 //another chunk of data has been recieved, so append it to `str`
  response.on('data', function (chunk) {
  str += chunk;
});

//the whole response has been recieved, so we just print it out here
  response.on('end', function () {
    console.log(str);
  });
}

http.request(options, callback).end();