Many thanks for your hint.
I could not reproduce step no. 4.
In DNN (Version 5.4.4) the link button has only the option to insert document links.
And the document manager shows the secured path but not the secured file.
My suggestion is: Why do you not offer this as feature in a new cart version?
I think this steps could be done through code?
I could do this steps, but could my customer do this, if he inserted his product?
Another suggestion is: if you buy the cart and the gatekeeper to secure files, you should get a special price.
Many thanks in advance