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.
document.blockUnblockOnload?.(false);
    
    this._unblockDocumentLoadEvent = () => {};
  },
  /**
   * @ignore
   */
  _reportDocumentStatsTelemetry() {
    const { stats } = this.pdfDocument;
    if (stats !== this._docStats) {
      this._docStats = stats;
      this.externalServices.reportTelemetry({
        type: "documentStats",
        stats,
      });
    }
  },
  /**
   * Used together with the integration-tests, to enable awaiting full
   * initialization of the scripting/sandbox.
   */
  get scriptingReady() {
    return this.pdfScriptingManager.ready;
  },
};
let validateFileURL;
if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
  const HOSTED_VIEWER_ORIGINS = [