I have no idea what you're trying to do and the variable names don't make any sense to me, but the following is a reformatted, simplified version of your script that is a valid bash script (and is easier for humans to read) that produces some output that may be what you want:

Code:

#!/bin/bash
fkt_auffuellen() {
        case $1 in
        (C)     if [ ${#2} -eq "$3" ]
                then    value="$2"
                else    value="$(printf "%-$3.$3s" "$2")"
                fi;;
        (N)     ;;
        (D)     ;;
        esac
}
vorg_nr_t=C
vorg_nr="AUFTRAG005-010010"
vorg_nr_l=40
fkt_auffuellen $vorg_nr_t $vorg_nr $vorg_nr_l
vorg_nr="$value"
echo "$vorg_nr"

Note that some double-quotes were added and others were removed, an if statement was removed by changing the printf format string, and I added opening parentheses to the case matching patterns. (The opening parentheses are allowed but are not required by bash, but if you're editing a larger script with an editor such as vi with a showmatch option, having them makes it much easier to find mismatched parentheses in places where they do matter.)

Hope this helps.