Implementing pdf call-back to server

I am a teacher using dynamic pdfs on my website that students can fill in. I wanted students to submit/save their work on my server so I can mark and I found the solution here in the forum from @Joel Geraci  https://codepen.io/practicalPDF/pen/eYBOpEm. However I could not make it work on my server as it requires PHP or similar code. Can anyone please guide on PHP code so I can complete this implementation.