Store your file in a Server folder rather in Database. Try with below snippet to force download the file. It means, You'll get a Download dialogue window even if file formats (Like Images, PDF etc.) could be opened within the Browser.
HTML
<a href="download.php">Download File</a>
download.php
<?php
$yourFile = "Your_Folder/YOUR_File.ext";
header('Content-Type: application/download');
header('Content-Disposition: attachment; filename='.$yourFile);
header("Content-Length: " . filesize($yourFile));
$fp = fopen($yourFile, "r");
fpassthru($fp);
fclose($fp);
?>