Custome field on Product page & Checkout

I am looking for help trying to get my products to display expiry dates and also put these into the checkout order which then shows on the pdf invoices.

So in the backend I put for example:

Expiry Date: 05/2021
Batch : 11000

Then this is displayed on the invoice. The expiry and batch needs to be displayed above the price on the product page near where it says product is available for back orders.

I don’t mind paying for development or a plugin.

Ive been losing my hair googling this as every site is trying to sell me a plugin that actually doesn’t do what I want with the checkout and location.