If you need to enable customers to attach files to a product before purchasing it, use the Customer File Uploads & Product Attachments add-on. A store administrator can then download the attached files when processing the order.
The add-on allows limiting the number and size of the files a customer can upload, enabling file attachments on a per-product basis and making them mandatory to place an order.
To install the add-on, follow the general instructions provided here.
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