Adding downloadable products is simple.

When you're creating a product and you reach the field where you're prompted to set the price, you will see a field below that with a checkbox that asks "is this product a downloadable one?"

Check that box, and add the URL link to your product. If it's a PDF file, the simplest way would be to add that digital product as a file in Google Drive, which will create a link for that document you can share.

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