Format( '%4.4d', [ 1 ] );

일껄요... 아마 ^^a;;

Format string 도움말을 보면

d     Decimal. The argument must be an integer value. The value is converted to a string of
      decimal digits. If the format string contains a precision specifier, it indicates that the
      resulting string must contain at least the specified number of digits; if the value has
      less digits, the resulting string is left-padded with zeros.

요렇게 되어 있어요.. ^^;;