Message is not displaying after downloading the file

Question

$msg=DisplayMsg();
if($msg)
{
try
{
$select = "SELECT * FROM `success-stories` where id='$id'";
$result = $conn->query($select);
$row = $result->fetch_assoc();
$file=$row["download_pdf"];
$file_arr=explode("/",$file);
$path=$file_arr[0]."/".$file_arr[1]."/".$file_arr[2];
if(file_exists($path))
{
header('Content-Description: File Transfer');
header('Content-Type: application/pdf');
header('Content-Disposition: attachment; filename="'.$path.'"');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($path));
ob_clean();
ob_flush();
readfile($path);
}
}
catch(Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
}
}

<?php
function DisplayMsg()
{
$val="";
try{
echo "<h4 class='alert alert-success'>Thank you for downloading story</h4>";
}
catch(Exception $e)
{

}
return $val="success";
}
?>