main.js

var printPDFBton = document.getElementById('print-pdf');
var ipc = require('electron').ipcRenderer;

printPDFBton.addEventListener('click', function (event) {
  ipc.send('print-to-pdf');
});

ipc.on('wrote-pdf', function (event, path) {
  // TODO should we open the pdf? or put it somewhere else?
  var message = 'Wrote PDF to: ~' + path;
  document.getElementById('pdf-path').innerHTML = message;
});

renderer.js

var fs = require('fs');
var BrowserWindow = require('browser-window');
var ipc = require('electron').ipcMain;
var shell = require('shell');

module.exports.setup = function () {
  ipc.on('print-to-pdf', function (event) {
    var pdfPath = '/tmp/print.pdf';
    var win = BrowserWindow.fromWebContents(event.sender);
    // Use default printing options
    win.webContents.printToPDF({}, function (error, data) {
      if (error) throw error;
      fs.writeFile(pdfPath, data, function (error) {
        if (error) {
          throw error;
        }
        shell.openItem(pdfPath);
        event.sender.send('wrote-pdf', pdfPath);
      });
    });
  });
};