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.
});
    }
    let formType = null;
    if (info.IsXFAPresent) {
      formType = "xfa";
    } else if (info.IsAcroFormPresent) {
      formType = "acroform";
    }
    this.externalServices.reportTelemetry({
      type: "documentInfo",
      version: versionId,
      generator: generatorId,
      formType,
    });
    this.eventBus.dispatch("metadataloaded", { source: this });
  },
  /**
   * @private
   */
  async _initializePageLabels(pdfDocument) {
    const labels = await pdfDocument.getPageLabels();
    if (pdfDocument !== this.pdfDocument) {
      return; 
    }
    if (!labels || AppOptions.get("disablePageLabels")) {
      return;
    }
    const numLabels = labels.length;