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.
this.pageNumber = pageNumber;
    this.pageLabel = pageLabel;
    this._updateUIState(false);
  }
  setPagesCount(pagesCount, hasPageLabels) {
    this.pagesCount = pagesCount;
    this.hasPageLabels = hasPageLabels;
    this._updateUIState(true);
  }
  setPageScale(pageScaleValue, pageScale) {
    this.pageScaleValue = (pageScaleValue || pageScale).toString();
    this.pageScale = pageScale;
    this._updateUIState(false);
  }
  reset() {
    this.pageNumber = 0;
    this.pageLabel = null;
    this.hasPageLabels = false;
    this.pagesCount = 0;
    this.pageScaleValue = DEFAULT_SCALE_VALUE;
    this.pageScale = DEFAULT_SCALE;
    this._updateUIState(true);
    this.updateLoadingIndicatorState();
    this.updateEditorModeButtonsState();
  }
  _bindListeners(options) {