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.
textLayerDiv,
    pageIndex,
    viewport,
    enhanceTextSelection = false,
    eventBus,
    highlighter
  ) {
    return new TextLayerBuilder({
      textLayerDiv,
      eventBus,
      pageIndex,
      viewport,
      enhanceTextSelection: this.isInPresentationMode
        ? false
        : enhanceTextSelection,
      highlighter,
    });
  }
  /**
   * @param {number} pageIndex
   * @param {EventBus} eventBus
   * @returns {TextHighlighter}
   */
  createTextHighlighter(pageIndex, eventBus) {