The download tag would not allow you to just show a URL if the order has been paid. You could however wrap the content within a {exp:store:orders}
tag pair then use the conditional {if is_order_paid}
to only show the content if the order has indeed been paid for.
Also I have seen in the past someone create similar functionality by adding a custom field to the content that they wanted to secure that basically had the entry_id of the product that could be purchased. So for example let say your product with an entry_id of 25 was purchased. That product granted access to some content in another channel, in the other channel you would need a field (playa, relationship, text fields or similar) that you entered the value 25 in. Then in your template you would need to write a custom query to search the exp_store_orders
tables for the currently logged in members orders then check the exp_store_order_items
for the corresponding ordered items to see if one of the items the currently logged in member purchased was indeed the entry_id that you specified earlier (in this case 25).
Having said that your best bet would be to extract that query into a little custom plugin instead of having that all at the template level.