Are there any specific PHP functions or methods that should be used to ensure the security and integrity of file downloads from a web server?

To ensure the security and integrity of file downloads from a web server, it is important to use PHP functions like `readfile()` and `header()` to properly handle the file download process. Additionally, you should validate user input to prevent directory traversal attacks and ensure that only authorized users can access the files.

<?php
$file = 'path/to/file.pdf';

if (file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/pdf');
    header('Content-Disposition: attachment; filename=' . basename($file));
    header('Content-Length: ' . filesize($file));
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    readfile($file);
    exit;
} else {
    echo 'File not found';
}
?>