I have an accessible and secure form script for my site with instructions, Ok so far. I am not familiar with doing PHP.

My site currently composed of .shtml pages. I want to add a PHP enquiry form (configuration rules provided for the form I have so I can fiddle to get the fields I want: senders address, name and text field, really simple) to my Office page.

My server allows PHP so do I need to do anything to get it to run?

I need to know what I need to do to the office.shtml to get it to run the PHP. This installation instruction is given:

"5. Using the PHP include function, include the file gbcf_form.php
in any *.php page file where you want it to be. It must be
below the <body> tag and preferably below the main heading.
I recommend placing it in the main content area.
See Example 1, below.
Example 1
<?php include("form-files-directory/gbcf_form.php"); ?>"

What do I do to my office.shtml file to get it to run the PHP. Change it to office.php?

Any other advice I've forgotten appreciated. Thanks.