Hi,
I was able to locate a tutorial that is similar to what you are looking for where you can view the code for an example for a product configurator here . The example allows visitors to customize a product and add it to the cart. You will have to customize the code a bit differently since you’re trying to upload a file.
If you are using Wix Stores, you can vote for this feature request here since it is not yet possible to add a file upload on the product page.
Best regards,
Edward