If your opencart product has a link demo, and need to have a links for each products, then you can use this mod.
with this mod you can input the url link demo in admin, and the demo link button will show up on featured, latest, bestseller, special modules, category, search, manufacturer info, special, and product pages.

Opencart compatibility: v1.5.6, v1.5.6.1, v1.5.6.2, v1.5.6.3, v1.5.6.4