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.
} catch (ex) {
            console.error(`_parseHashParameters: "${ex.message}".`);
          }
          break;
      }
    }
    if (params.has("pdfbug")) {
      AppOptions.set("pdfBug", true);
      AppOptions.set("fontExtraProperties", true);
      const enabled = params.get("pdfbug").split(",");
      try {
        await loadPDFBug(this);
        this._PDFBug.init({ OPS }, mainContainer, enabled);
      } catch (ex) {
        console.error(`_parseHashParameters: "${ex.message}".`);
      }
    }
    
    if (
      (typeof PDFJSDev === "undefined" ||
        PDFJSDev.test("!PRODUCTION || GENERIC")) &&
      params.has("locale")
    ) {
      AppOptions.set("locale", params.get("locale"));
    }
  },
  /**
   * @private
   */
  async _initializeL10n() {