Based on this answer, to have the customer email address, I edited the $shippingAddress in app/code/core/Mage/Sales/Model/Order/Pdf/Abstract.php like below, but it makes the shipping section in pdf show nothing.
The customer is NOT LOGGED IN, does it matter? how to fix this?
$shippingAddress = $this->_formatAddress($order->getShippingAddress()->format('pdf')).'|'.Mage::helper('sales')->__('Email:').$order->getCustomerEmail();
I'm wondering if .'|'.Mage::helper('sales')->__('Email:').$order->getCustomerEmail(); is correct?