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.
scale = 1;
          break;
        case "page-width":
          scale = pageWidthScale;
          break;
        case "page-height":
          scale = pageHeightScale;
          break;
        case "page-fit":
          scale = Math.min(pageWidthScale, pageHeightScale);
          break;
        case "auto":
          
          
          const horizontalScale = isPortraitOrientation(currentPage)
            ? pageWidthScale
            : Math.min(pageHeightScale, pageWidthScale);
          scale = Math.min(MAX_AUTO_SCALE, horizontalScale);
          break;
        default:
          console.error(`_setScale: "${value}" is an unknown zoom value.`);
          return;
      }
      this._setScaleUpdatePages(scale, value, noScroll,  true);
    }
  }
  /**
   * Refreshes page view: scrolls to the current page and updates the scale.
   */
  #resetCurrentPageView() {