Need to add php code to speicfic pages

Have a client that sent us over stand alone .php pages for a 5 part form that needs verification along the way as it is filled out (we are reconstructing these pages in a new WP site for them). I am trying to find out how we can add the following code below to the header area above </head>. Plugins we have tried do not do the job. Any advice on the best way to do this for specific pages is much appreciated (there is different code for all 5 pages in the head area):

<?php

include_once __DIR__.’/FX/FX.php’;
include_once __DIR__.’/FX/FX_Error.php’;
include_once __DIR__.’/FX/server_data.php’;
require_once __DIR__.’/FX/image_proxy.php’;

// suppress PHP notices
ini_set(‘display_errors’,’Off’);

$vendorName=$_POST[“vendorName”];
$billingCode=$_POST[“billingCode”];
$reportEmail=$_POST[“reportEmail”];

$fullName=$_POST[“fullName”];
$address=$_POST[“address”];
$address2=$_POST[“address2”];
$city=$_POST[“city”];
$state=$_POST[“state”];
$zipCode=$_POST[“zipCode”];
$phone=$_POST[“phone”];
$altPhone=$_POST[“altPhone”];
$email=$_POST[“email”];

$successFlag=TRUE;
if (is_object($search1Result)) {
if ($search1Result->code == 401) {
//echo ‘isObject_401(‘.$search1Result->code.’)’;
$successFlag=FALSE;
}
} else if ($search1Result[‘errorCode’] == 401) {
//echo ‘notAnObject_401(‘.$search1Result[‘errorCode’].’)’;
$successFlag=FALSE;
} else {
//echo ‘passedBoth401Tests(‘.$search1Result[‘errorCode’].’)’;
}

// Pull the ContractorID
foreach($search1Result[‘data’] as $key=>$search1Data) {
$contractorID=$search1Data[‘id’][0];
}

?>