foreach($_POST['visitProperty'] as $check) {
        $fileName = "pdata.txt";
        $fileContent = file($fileName);
        $readFile = fopen($fileName, "w+");
        $fileContent[$check] = "TEST TO SEE IF LINE REPLACED";
        $update = fwrite($readFile, $fileContent[$check]);
        fclose($readFile);
    }

$fileName = "pdata.txt";
$fileContent = file($fileName);
foreach($_POST['visitProperty'] as $check) {
    $fileContent[$check] = "TEST TO SEE IF LINE REPLACED";
}
file_put_contents ($fileName, implode("n", $fileContent));