my %jabb = do {
    open my $fh, '<', '/path/to/jabb.txt'
        or die $!;
    map { reverse split; } <$fh>;
};

my $re = do {
    local $" = '|';
    qr!\b(@{[map { qr/\Q$_\E/ keys %jabb]})\b!;
};

open my $in,  '<', '/another/path/to/input.txt'
    or die $!;
open my $out, '>', '/the/path/to/output.txt'
    or die $!;

while (<$in>) {
    s/$re/$jabb{$1}/g;
    print $out $_;
}