Since #12241 we have notifications for this when the user navigates away from the viewer, but we do not yet warn when switching documents, which means that if you call e.g. `PDFViewerApplication.open` with a new document (or directly call `BaseViewer.setDocument` when using the viewer components standalone) there won't be any warning about losing form data. This should be addressed.
return this.pdfViewer.currentPageNumber;
  },
  set page(val) {
    this.pdfViewer.currentPageNumber = val;
  },
  get supportsPrinting() {
    return PDFPrintServiceFactory.instance.supportsPrinting;
  },
  get supportsFullscreen() {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      return shadow(this, "supportsFullscreen", document.fullscreenEnabled);
    }
    const doc = document.documentElement;
    let support = !!(
      doc.requestFullscreen ||
      doc.mozRequestFullScreen ||
      doc.webkitRequestFullScreen
    );
    if (
      document.fullscreenEnabled === false ||
      document.mozFullScreenEnabled === false ||
      document.webkitFullscreenEnabled === false
    ) {
      support = false;
    }
    return shadow(this, "supportsFullscreen", support);
  },
  get supportsIntegratedFind() {