For most file formats, if you click on them to download them then they will open in a new tab - e.g. PDF files. This is not always what is required.

This behavior can easily be prevented - the only requirement is that the Apache mod_headers module is activated. If this module is available in your setup, just insert a .htaccess file with the following content:

<FilesMatch "\.(?i:pdf|jpg|gif)$">
 ForceType application/octet-stream
 Header set Content-Disposition attachment
</FilesMatch>