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 currentPageNumber = this._currentPageNumber,
      pagesCount = this.pagesCount;
    if (currentPageNumber >= pagesCount) {
      return false;
    }
    const advance =
      this._getPageAdvance(currentPageNumber,  false) || 1;
    this.currentPageNumber = Math.min(currentPageNumber + advance, pagesCount);
    return true;
  }
  /**
   * Go to the previous page, taking scroll/spread-modes into account.
   * @returns {boolean} Whether navigation occured.
   */
  previousPage() {
    const currentPageNumber = this._currentPageNumber;
    if (currentPageNumber <= 1) {
      return false;
    }
    const advance =
      this._getPageAdvance(currentPageNumber,  true) || 1;
    this.currentPageNumber = Math.max(currentPageNumber - advance, 1);
    return true;
  }
  /**
   * Increase the current zoom level one, or more, times.
   * @param {number} [steps] - Defaults to zooming once.
   */
  increaseScale(steps = 1) {