How I can replace an acroform PDF field with text using PHP

I have a PDF using AcroForm. I want once the form is filled to replace the form with the fixed value. My reason is that I want to autofill a PDF then send it to an another person via mail without being able the one that opens it be able to edit it.

So I want to ask how I can either lock an Acroform PDF form so it can be prevented from editing or how I can replace the acroform field with its value.