my_pmprorh_init.php

<?php
/**
 * Add the code below to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
//we have to put everything in a function called on init, so we are sure Register Helper is loaded
function my_pmprorh_init()
{
	//don't break if Register Helper is not loaded
	if(!function_exists( 'pmprorh_add_registration_field' )) {
		return false;
	}
	
	//define the fields
	$fields = array();
	$fields[] = new PMProRH_Field(
		'company',						// input name, will also be used as meta key
		'text',							// type of field
		array(
			'label'		=> 'Company',		// custom field label
			'class'		=> 'company',			// custom class
			'profile'	=> true,			// show in user profile
			'required'	=> true,			// make this field required
		)
	);
	
	//add the fields into a new checkout_boxes are of the checkout page
	foreach($fields as $field)
		pmprorh_add_registration_field(
			'checkout_boxes',				// location on checkout page
			$field						// PMProRH_Field object
		);
	//that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( 'init', 'my_pmprorh_init' );