There are several possibilities to track downloaded files.
Serve through PHP
* breaks with caching
* probably way out of scope for Statify
Intercept through PHP with redirect to real file
* can get tricky with caching, but possible
* does not accurately track number of downloads, only number of redirections to the actual link
* also way out of scope for Statify
Intercept with JavaScript
* only works with JS tracking
* can get tricky on which links the interception should be appended and which not
* does not actually track downloads, but clicks on the link
All assuming you use default WP file management. There are several Download manager or monitoring Plugins available for WordPress which provide such features. I don’t think such feature is really suitable for Statify
Regards,
Stefan