Hide some document categories for non members (woocommerce product docs)

Hi

Im looking for something that I think is quite simple but I just cant figure out how to do it.
So I have woothemes plugin “Product Documents” and would like to hide some of the documents for people that is not logged in.
Lets say that I have a document category called “Service” and one called “Secret” that I want to only show when logged in, how would I implement that?
I have a code to hide all, but how do I only hide some categories/documents?

This is the code I have for functions.php (from woothemes page)

add_filter( 'wc_product_documents_get_sections', 'show_documents_only_for_logged_in_users', 10, 3 );

/**
 * Don't return document sections unless there is a logged in user.
 *
 * @param array $sections array of sections
 * @param WC_Product_Documents_Collection $collection the collection object
 * @param boolean $include_empty whether to include empty sections in the result
 * @return array sections for display
 */
function show_documents_only_for_logged_in_users( $sections, $collection, $include_empty ) {

    // this check can be made as specific (by user role, etc) as desired
    if ( ! get_current_user_id() ) {
        return array();
    }

    return $sections;
}

Thanks a lot in advance!
Best regards
Max