Can customers add personal details to pre-designed products online?

Thank you so much for such a quick response. I appreciate it so much. Unfortunately this wont work because my store is a print on demand.

I need more of a way to have them choose from their fonts etc they already have on Shopify.

In my mind, they would just click on a button to add a number and name themselves on the back and whatever font they use or choose would be printed. The POD company wont just assume the design after the order is placed.

You are a rockstar though. Thank you so much!