.php

<?php
 
// place this code inside a php file and call it f.e. "download.php"
$path = $_SERVER['DOCUMENT_ROOT']."/path2file/"; // change the path to fit your websites document structure
$fullPath = $path.$_GET['download_file'];
 
if ($fd = fopen ($fullPath, "r")) {
    $fsize = filesize($fullPath);
    $path_parts = pathinfo($fullPath);
    $ext = strtolower($path_parts["extension"]);
    switch ($ext) {
        case "pdf":
        header("Content-type: application/pdf"); 
        header("Content-Disposition: attachment; filename=\"".$path_parts["basename"]."\""); // use 'attachment' to force a download
        break;
        default; // Other document formats (doc, docx, odt, ods etc)
        header('Content-type: application/vnd.openxmlformats-officedocument.wordprocessingml.document');
        header("Content-Disposition: filename=\"".$path_parts["basename"]."\"");
    }
    
    header('Content-Description: File Transfer');
    header('Content-Transfer-Encoding: binary');
    header('Connection: Keep-Alive');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');

    ob_clean();
    flush();
    readfile($fullPath);
}
fclose ($fd);
exit;
// example: place this kind of link into the document where the file download is offered:
// <a href="download.php?download_file=some_file.pdf">Download here</a>
?>