Here are the materials I used:

Paper: https://www.amazon.com/dp/B09B8N675X?psc=1&ref=ppx_yo2_dt_b_product_details

Fountain pen: https://www.amazon.com/dp/B07SNFK6TP?psc=1&ref=ppx_yo2_dt_b_product_details

Sealing wax: https://www.amazon.com/dp/B078H9H1V6?psc=1&ref=ppx_yo2_dt_b_product_details

Seal: from MakeYourCraft shop on Etsy

(These are just recommendations, I don't benefit from sales of these items.)