php从第5个字母到第6个字母读取txt文件

I'd like to read letters from txt file, but only from 5th to 6th (2 letters)

<?  $myFile = "administrator/data.txt"; 
    $fh = fopen($myFile, 'r'); 
    $theData = fread($fh, 4); 
    fclose($fh); 
?>

This code reads the first 4 numbers, but I don't know how to choose letters from 5th to 6th letter.

Use fseek to advance the file pointer to the desired position first.

...
fseek($fh, 5);
$theData = fread($fh, 2);
...