title: Display "download now" on products that have 0 price prestashop 1.7
body: <p>ps 1.7</p>
  <p>I have a virtual store , and i want to change &quot;add to cart&quot; button to &quot;download now&quot; when price is zero . my mean , For free products, change the &quot;Add to Cart&quot; button to the &quot;Download&quot;</p>
  <p>i used this in product.tpl:</p>
  <pre><code>        {if $product-&gt;price &lt;= 0}
          {l s='Download now'}
          {else}
          {l s='Add to cart' d='Shop.Theme.Actions'}
          {/if}
  </code></pre>
  <p>but not worked,
  so how can i fix that ?</p>