Making the 'add to cart' button redirect to PayPal

create a paypal smart button(buy or add to cart) from paypal.com and paste the HTML code in the website (in HTML )..on click, it will redirect to Paypal page for login and payment processing.its a simple process.

A solution can be found in the function woocommerce_add_to_cart_action. We have to chain two filters. In the first, we check for the product ID, if it's one of a list we add the redirect.

add_action( 'woocommerce_add_to_cart_validation', 'check_ids_wpse_119466', 10, 3 );

function check_ids_wpse_119466( $true, $product_id, $quantity ) 
{
    # Not our products, bail out
    # Adjust the products IDs
    if( !in_array( $product_id, array( 1306,1303 ) ) ) // <------ ADJUST LIST
        return $true;

    add_filter( 'add_to_cart_redirect', 'redirect_wpse_119466' );
    add_filter( 'allowed_redirect_hosts', 'whitelist_wpse_119466' );
    return $true;
}

function redirect_wpse_119466( $url )
{
    return 'http://paypal.com';
}

function whitelist_wpse_119466( $hosts )
{
    $hosts[] = 'paypal.com';
    return $hosts;
}

There's a third filter that we need to add, and it tells WordPress that PayPal is a safe host to redirect.

Yes, the list of products has to be made by hand. Or add an option somewhere in the theme, in a plugin or even WordPress settings to put this values (with a multiple selection field).

_{Related: Where do I put the code snippets I found here or somewhere else on the web?}