how add value to Order Custom Field by hook

[hogava]

Hi

I want add a value to "Custom Field" of product, during order process.

how i can do this with hook?

[hogava]

Exactly I want to add a value to a product custom field when invoice paid, that shown in order or invoice page.

Thanks for your help.

<?php

add_hook('InvoicePaid', 1, function($vars) {

    // Perform hook code here...

});