Hi Eric,
Firstly, many thanks for your help on this.
I've done as you ask and the result, unfortunately, is the same.
This is the adapted code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Download test</title>
</head>
<body>
<?php
$fileName = "wemmicks.pdf"; //the name of the file, example: yourfile.pdf
$path = "http://billericaybaptist.net/av-files/sermon-attachments/" . $fileName; //the file system path to the file, example: C:\\Inetpub\\wwwroot\\
header('Cache-Control:');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="' . $fileName . '"');
//these next four lines are not in the DFP code
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
//down to here
header("Content-length: ".filesize($path));
//these next two lines are not in the DFP code also
ob_clean();
flush();
// to here
readfile("$path");
?>
</body>
</html>