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.
const { pageNumber } = this.items;
    pageNumber.classList.toggle(PAGE_NUMBER_LOADING_INDICATOR, loading);
  }
  updateEditorModeButtonsState(disabled = false) {
    const { editorNoneButton, editorFreeTextButton, editorInkButton } =
      this.items;
    editorNoneButton.disabled = disabled;
    editorFreeTextButton.disabled = disabled;
    editorInkButton.disabled = disabled;
  }
  /**
   * Increase the width of the zoom dropdown DOM element if, and only if, it's
   * too narrow to fit the *longest* of the localized strings.
   */
  async #adjustScaleWidth() {
    const { items, l10n } = this;
    const predefinedValuesPromise = Promise.all([
      l10n.get("page_scale_auto"),
      l10n.get("page_scale_actual"),
      l10n.get("page_scale_fit"),
      l10n.get("page_scale_width"),
    ]);
    await animationStarted;
    const style = getComputedStyle(items.scaleSelect),
      scaleSelectContainerWidth = parseInt(