Im looking to create a webshop where my customer in step 1 choose a product and in step 2 they have to upload me a picture and in step 3 they pay in paypal.
In admin i need to se if they paid and save down their picture to the computer.
Yes it's possible. The upload of files during the checkout or on the product page can be done with custom fields (menu Display->Custom fields) of the table "order" or "item" and of the type "file" (Business edition only).