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.
y = pageHeight;
        }
        break;
      case "FitV":
      case "FitBV":
        x = destArray[2];
        width = pageWidth;
        height = pageHeight;
        scale = "page-height";
        break;
      case "FitR":
        x = destArray[2];
        y = destArray[3];
        width = destArray[4] - x;
        height = destArray[5] - y;
        const hPadding = this.removePageBorders ? 0 : SCROLLBAR_PADDING;
        const vPadding = this.removePageBorders ? 0 : VERTICAL_PADDING;
        widthScale =
          (this.container.clientWidth - hPadding) /
          width /
          PixelsPerInch.PDF_TO_CSS_UNITS;
        heightScale =
          (this.container.clientHeight - vPadding) /
          height /
          PixelsPerInch.PDF_TO_CSS_UNITS;
        scale = Math.min(Math.abs(widthScale), Math.abs(heightScale));
        break;
      default:
        console.error(
          `scrollPageIntoView: "${destArray[1].name}" is not a valid destination type.`