If you hope to sell PDF patterns, then you may be interested in using Digital Downloads - The app was developed by Shopify and is free to use. You can learn more about Digital Downloads through our help centre here.
You may find our Intro to Shopify document helpful in providing more information on what we offer. You can also sign up for our free Shopify course which will guide you through the steps on setting up your store.
I know setting up a new store and business can be daunting. Please don't hesitate to let me know if you have any other questions as I'd be happy to help!