One way:

use warnings;
use strict;

while (<DATA>) {
    chomp;
    my $len = length;
    $_ .= ' ' x (76 - $len) if $len < 76;
    print "$_\n";
}

__DATA__
hfgjjasdgasdhgfask
jhagfghfjkhsdg
fjhsdfj
fsf
[download]