chomp( my @file1 = do { open FH, (+shift); <FH> } );
chomp( my @file2 = do { open FH, (+shift); <FH> } );

my @file3;
while( @file1 && @file2)
{
    push @file3, join(' ', shift(@file1), shift(@file2));
}

open FH, ">output";
print FH join($/, @file3, '');
close FH;