How to use api dpd co uk api integration with php

Question

I have been assigned the task of integrating a shipping company's API with a client's website and I want to know about its API documentation. I have the pdf that client has shared but I am not able to understand that much from it. 

The code I tried:

$url="api.dpd.co.uk/user/?action=login HTTP/1.1";

$options = array(

    'http' => array(

        'method' => 'POST',

        'Host' => 'api.dpd.co.uk',

        'method' => 'POST',

        'header'=> "Content-Type: application/json\r\n" .

                    "Accept: application/json\r\n".

                    "Authorization: Basic RFNNSVRIOk1ZUEFTU1dE".

                    "GEOClient:".base64_encode("account/123456").

                    "Content-Length: 0"

      )

);

$context = stream_context_create($options);

$result = file_get_contents($url, false, $context);

$response = json_decode($result);

echo var_dump($response);

Can someone help me with this?