You can try something like this.

#!/usr/bin/perl

use strict;

while (<DATA>) {
    if (/\.\.DN:\n/ ... /(\w+)\n/ ) {
        print "$1\n" if $1;
    }
}

__DATA__
..DN:
000044255
..CB:
..SN:
D046H6J5
..PD:
20091030
..DD:
Friday, October 30, 2009
..PY:
2009
..ED:
..DN:
000044254
..CB:
..SN:
D046H6IR
..PD:
20091030
..DD:
Friday, October 30, 2009
..PY:
2009
..ED:
[download]