Allows to pull pdf.js from pdf_viewer using require().

web/pdfjs.js

@@ -12,13 +12,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* globals module */
+/* globals module, __pdfjsdev_webpack__ */
 /* umdutils ignore */
 
 'use strict';
 
 if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('PRODUCTION')) {
-  module.exports = window['pdfjs-dist/build/pdf']; // loaded via html script tag
+  var pdfjsLib;
+  // The if below protected by __pdfjsdev_webpack__ check from webpack parsing.
+  if (typeof __pdfjsdev_webpack__ === 'undefined') {
+    if (typeof require === 'function') {
+      pdfjsLib = require('../build/pdf.js'); // using a bundler to pull the core
+    } else {
+      pdfjsLib = window['pdfjs-dist/build/pdf']; // loaded via html script tag
+    }
+  }
+  module.exports = pdfjsLib;
 } else {
   (function (root, factory) {
     if (typeof define === 'function' && define.amd) {