This type of file download script I have used in most of my web application. When you want to download any file you need to send the file name to this application, rest of the thing PHP will handle.
File list:
files
....\make-Zip-in-PHP.jpg

....\PHP-file-download-script.jpg

....\tick.jpg

....\webinfopedia.com.docx
....\webinfopedia.txt
download.php
index.php