Hi,
again, you did not provide any sample code. This makes it extremely difficult to guess what you actually want or what your problem is.
Furthermore, you leave all the work of creating some sample code to explain something to us.
Regarding your question: I can only guess that you did not properly name your form elements.

$product=param($product);
[download]

works if there is a form element with a name property of $product and the submit button has been clicked.
If you give us an example, we can look at the code and tell you more.
Regards,
svenXY