$args = array(
'post_type' => 'product',
'tax_query' => array(
array(
'taxonomy' => 'product_cat',
'field' => 'id',
'terms' => $cat_id
),
array(
'taxonomy' => 'product_visibility',
'field' => 'slug',
'terms' => 'exclude-from-catalog', // Possibly 'exclude-from-search' too
'operator' => 'NOT IN'
)
)
);
$query = new WP_Query( $args );
<button type="submit" value="Сделать заказ" class="botton_form h4" onclick='
if (document.getElementById("tel").value == "")
{
window.open("images/сертификат.pdf", "_blank");
}'>Скачать сертификат</button>