Using zencart to allow customers to purchase digital download books/pdfs
is possible..Using zencart mod to integrate Amazon products is not available at moment...
only way to do it would be link products to amazon website, via zencart product description facilities.
There is a drop ship module for zencart in downloads section at zencart
forums..
Suggest you download latest copy of zencart, install and opt for demo products to be added..
you will then see what zencart is capable of
i.e. Demo zencart at
http://www.zencart.net/demo/