I need to add 1 extra data with prestashop order but I can't find any way to do it like in wordpress we can add extra fields.
Actually I've new module for payment gateway and it saves order to that payment gateway server and create their own id so I would like to save that id with my prestashop order so when I cancel order I can call one api to cancel it on my server as well.
You must edit your payment module and add the fields you want to the module database.
Changing the PrestaShop Core (and database) is not a good thing and is not recommended.
The best and the cleanest is to create a new table that will contain the Prestashop order idea, and the additional payment identifier.
Regards