open(INPUT, "data.txt") || die "Error opening 'keywd.txt'\n";
             ^^^^----------- wtf? -------------^^^^^ 

##</code><code>##

open(FH, '<', "keywd.txt") || die "Error opening 'data.txt'\n";

##</code><code>##

open(FH, '<', "keyword.txt") || die "Error opening 'keyword.txt': $!\n";
                   ^^-- sic!     error message in here -----------^^

##</code><code>##

chomp(my @data = <INPUT>);