Oblige to download PDF

On my site teams can download a PDF with an editable application form. After filling in this form, there is a button to submit the form.

In Adobe this works perfectly but when the file is clicked on my site, it opens in the browser. And the submit form button does not work (for some browsers).

Question: what is the code to make sure that the file must be downloaded to the computer and will not open in the browser?