PHP script to submit form at a URL and receive/save downloaded file to server

Hello, At this URL ([login to view URL]), at the bottom there is a submit button (next to text "Формат за изтегляне") with a dropbox selected at XLS and submit. When clicking the button, the result is a file being downloaded. The project is a php script to run from a cron job, that will go to that page, click the submit (with value XLS remaining as it is) and take/accept the downloaded file and store it locally on the server. That's all. I've had trouble finding how to download it with a script, so i'm outsourcing. Please accept only if you are sure you can do it. Look at the code in the link, to get any other info you may need. Thanks!