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.
spread.className = "spread";
            viewer.append(spread);
          } else if (i % 2 === parity) {
            spread = spread.cloneNode(false);
            viewer.append(spread);
          }
          spread.append(pages[i].div);
        }
      }
    }
    if (!pageNumber) {
      return;
    }
    
    
    
    if (this._currentScaleValue && isNaN(this._currentScaleValue)) {
      this._setScale(this._currentScaleValue, true);
    }
    this._setCurrentPageNumber(pageNumber,  true);
    this.update();
  }
  /**
   * @private
   */
  _getPageAdvance(currentPageNumber, previous = false) {
    switch (this._scrollMode) {
      case ScrollMode.WRAPPED: {
        const { views } = this._getVisiblePages(),
          pageLayout = new Map();