You can simply download any file with downloader class. Simply pass file path to download the file as below.
use Cygnite\Common\Downloader; $download = new Download; $download->file('your/file/path');
Downloader allows you to download different kind of files.
Few extensions are - jpeg, jpg, gif,png, pdf, docx, zip, xls, video formats etc.
[Note: You can only download the files which are available inside framework root directory. But you may have multiple sub directories inside.]