displaying Leading Zeros for file count in a book? without hacking?

That format is often used in ATA (airlines) and MIL-SPEC (govt/military) docs.

Are you trying to develop support for something like this?

Structured solutions are available commercially for many of those standards. 

-Matt

You may have a look into my website https://www.daube.ch/docu/fmaker88.html. In the FMjsxLib there is a function FormatValue with this snippet:

   case "J":
      if (value > 0) {
        value = (Math.floor (value));
      } else {
        value = (Math.ceil (value));
      }
      sResult = KLD_Z.PadWith0(value, fmtSize);
      return sResult;

The function PadWith0 is this

KLD_F.PadWith0 = function (number, nPlaces) { // ================================
/*            Pad figures with leading zeroes
Arguments     number: any positive number
              nPlaces: resulting length after padding
Returns       Function value =  string: padded number: 7,2 => 07; 1234,3 => 1234
Comment       If nPlaces is insufficient, the last figure will become a ?
              Negative numbers are rejected as NaN.
Called by     FormatValue, GetTmpVarName
History       < 2019
*/
var j, jMax, sResult;

  if (number < 0) {return NaN;}
  sResult = number;
  if (typeof number == "number") {
    sResult = String(number);
  }
  jMax = nPlaces - sResult.length;
  if (jMax < 0 ) {
    sResult = sResult.substr (0, nPlaces - 1) + "?";
  } else {
    for (j = 0; j < jMax; j++) {
      sResult = '0' + sResult;
    }
  }
  return sResult;
} //--- end PadWith0 -----------------------------------------------------------------

It still requires hacking. You can go to https://tracker.adobe.com and put in a feature request. If you want a scripting solution, please contact me offlist.