**Please do not work on this issue unless you have applied to the outreachy project.**

The [pageviewer.js](https://github.com/mozilla/pdf.js/blob/master/examples/components/pageviewer.js) example currently uses the older style of `promise.then` and callbacks. Convert it to use an `async` function and `await` style.

cMapUrl: CMAP_URL,
  cMapPacked: CMAP_PACKED,
  enableXfa: ENABLE_XFA,
});
loadingTask.promise.then(function (pdfDocument) {
  
  return pdfDocument.getPage(PAGE_TO_VIEW).then(function (pdfPage) {
    
    const pdfPageView = new pdfjsViewer.PDFPageView({
      container,
      id: PAGE_TO_VIEW,
      scale: SCALE,
      defaultViewport: pdfPage.getViewport({ scale: SCALE }),
      eventBus,
      
      textLayerFactory: !pdfDocument.isPureXfa
        ? new pdfjsViewer.DefaultTextLayerFactory()
        : null,
      annotationLayerFactory: new pdfjsViewer.DefaultAnnotationLayerFactory(),
      xfaLayerFactory: pdfDocument.isPureXfa
        ? new pdfjsViewer.DefaultXfaLayerFactory()
        : null,
      structTreeLayerFactory: new pdfjsViewer.DefaultStructTreeLayerFactory(),
    });
    
    pdfPageView.setPdfPage(pdfPage);
    return pdfPageView.draw();
  });
});