phpBB File Download Extension

Install

Download the latest release.
Unzip the downloaded release, and change the name of the folder to filedownload.
In the ext directory of your phpBB board, create a new directory named dmzx (if it does not already exist).
Copy the filedownload folder to phpBB/ext/dmzx/ (if done correctly, you'll have the main extension class at (your forum root)/ext/dmzx/filedownload/composer.json).
Navigate in the ACP to Customise -> Manage extensions.
Look for File Download under the Disabled Extensions list, and click its Enable link.

Navigate in the ACP to Customise -> Extension Management -> Extensions.
Look for File Download under the Enabled Extensions list, and click its Disable link.
To permanently uninstall, click Delete Data and then delete the /ext/dmzx/filedownload folder.