Hi,
In the "files" area of a product, you have two buttons. The first button is an upload button so that you can select a file.
The second button will open a popup with a form where you can either upload a file or specify a location. And as the location path, you can either enter:
- a relative path from the upload secure folder of HikaShop
- a URL
So you can enter your link like that and it will appear as a download link. When you click on it, the download link with then redirect to the URL you entered.