title: How do I open a file with the default application
body: <p>I am downloading a file from DropBox.</p>
  
  <p>I can see that the file exists by using <code>File.exists(filePath)</code> and it returns <code>true</code>.
  But I am not able to open the file (with the default application) with either <code>File.fromPath(filePath)</code> or with <code>openUrl(filePath)</code>. </p>
  
  <p>Here is my code:</p>
  
  <pre><code>HomePage.prototype.getDownload = function() {
  var filePath = fs.path.join(fs.knownFolders.currentApp().path, "MyFile");
  
  httpModule.getFile({
      url: "https://content.dropboxapi.com/2/files/download",
      method: "POST",
      headers: { "Content-Type": "", "Dropbox-API-Arg": JSON.stringify({"path": "/MyFolder/MyFile"}), "Authorization": "Bearer *********" },      
  }, filePath).then(function (response) {
      console.log("file exists: "+fs.File.exists(filePath)); // This return true
      // tried this
      fs.File.fromPath(filePath); // Does nothing
      // tried this
      utilsutils.openUrl(filePath); // Does nothing
  }
  </code></pre>