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.
userOptions[name] = value;
  }
  static setAll(options) {
    for (const name in options) {
      userOptions[name] = options[name];
    }
  }
  static remove(name) {
    delete userOptions[name];
  }
  /**
   * @ignore
   */
  static _hasUserOptions() {
    return Object.keys(userOptions).length > 0;
  }
}
export { AppOptions, compatibilityParams, OptionKind };