We could use:
https://github.com/mozilla/pdf.js/blob/c3d08580627471432a6ad0b2fdb948df64126afa/src/display/api.js#L929

and look at bit 4.

The following pdf:
https://orimi.com/pdf-test.pdf
is not editable in neither Acrobat nor Edge nor Foxit and nor Okular.
});
    this.pdfSidebar.onToggled = this.forceRendering.bind(this);
    this.pdfSidebarResizer = new PDFSidebarResizer(
      appConfig.sidebarResizer,
      eventBus,
      this.l10n
    );
  },
  run(config) {
    this.initialize(config).then(webViewerInitialized);
  },
  get initialized() {
    return this._initializedCapability.settled;
  },
  get initializedPromise() {
    return this._initializedCapability.promise;
  },
  zoomIn(steps) {
    if (this.pdfViewer.isInPresentationMode) {
      return;
    }
    this.pdfViewer.increaseScale(steps);
  },
  zoomOut(steps) {
    if (this.pdfViewer.isInPresentationMode) {
      return;
    }
    this.pdfViewer.decreaseScale(steps);
  },
  zoomReset() {