Work with Amazon S3 plugin?

This is not a planned feature for the free version of this plugin nor a current feature of the premium version. But I would like to at some point incorporate it.

So you’re saying that the file has to be stored in the normal uploads folder for it to work?

The file needs to be stored on the same domain as the Woo installation.

Is it protected there from link sharing?

There are several ways to hide your uploads. Here is one: https://www.sellwithwp.com/how-to-create-woocommerce-secure-downloads/