Oro plaform is flexible system which give ability to customize CRUD page in admin for example you can add a custom section to edit order page and add new form or show custom details .

Let’s start by adding you service :

 
    ibnab_customsection_order.event_listener.order_edit_view_listener:
        class: 'Ibnab\Bundle\CustomSectionBundle\EventListener\OrderEditViewListener'
        arguments:
            - '@translator'
        tags:
            - { name: kernel.event_listener, event: oro_ui.scroll_data.before.order-edit, method: onEdit }
 

Here we handle kernel.event_listener of type oro_ui.scroll_data.before.order-edit to observe and inject of custom section to edit order page by the method  onEdit , 

The content of our class which contain  onEdit function:

 
<?php
namespace Ibnab\Bundle\CustomSectionBundle\EventListener;
use Oro\Bundle\UIBundle\Event\BeforeListRenderEvent;
use Symfony\Contracts\Translation\TranslatorInterface;
use Oro\Bundle\UIBundle\View\ScrollData;
class OrderEditViewListener {
    const CUSTOMSECTION_BLOCK_ID = 'customsection';
    /** @var int */
    const BLOCK_PRIORITY = 100;
    /**
     * @var TranslatorInterface
     */
    protected $translator;
    /**
     * @param TranslatorInterface $translator
     */
    public function __construct(TranslatorInterface $translator) {
        $this->translator = $translator;
    }
    /**
     * @param BeforeListRenderEvent $event
     */
    public function onEdit(BeforeListRenderEvent $event) {
        $entity = $event->getEntity();
        if ($entity != '''') {
            $template = $event->getEnvironment()->render(
                    'IbnabCustomSectionBundle:Order:update_order.html.twig', ['entity' => $entity,'form' => $event->getFormView()]
            );
            $this->addCustomSectionBlock($event->getScrollData(), $template);
        }
    }
    /**
     * @param ScrollData $scrollData
     * @param string $template
     */
    private function addCustomSectionBlock(ScrollData $scrollData, $template) {
        $scrollData->addNamedBlock(self::CUSTOMSECTION_BLOCK_ID, $this->translator->trans('ibnab.customsection.order.sections.customsection.label'), self::BLOCK_PRIORITY);
        $subBlock = $scrollData->addSubBlock(self::CUSTOMSECTION_BLOCK_ID);
        $scrollData->addSubBlockData(self:: CUSTOMSECTION_BLOCK_ID $subBlock, $template, self::CUSTOMSECTION_BLOCK_ID);
    }
}
​

You can explore  onEdit function which receive as param $event of type  Oro\Bundle\UIBundle\Event\BeforeListRenderEvent which give you ability for example to get current entity by $event->getEntity();  or form by $event->getForm();  so in this section we will render a twig  IbnabCustomSectionBundle:Order:update_order.html.twig and pass to variables $entity and $form, and we finish by call internal method of class  addCustomSectionBlock to add block section with method addNamedBlock of object ScrollData $scrollData , the I of block is  self::CUSTOMSECTION_BLOCK_ID and has a label for tab , after that we add a subBlock = content of block with same id and the result of twig $template .

let’s add our twig template IbnabCustomSectionBundle:Order:update_order.html.twig the full path is Ibnab/Bundle/CustomSectionBundle/Resources/views/Order/ update_order.html.twig an for example the content is :

 
{{ form_row(form.paymentDate) }}
 

for example you custom field  paymentDate whicch get added by migration and from and you can manage save value by form extension