If a customer did not receive a .pdf copy of their quote or invoice from a business email, this means it was likely sent from the customer profile - and not inside an order.  
​In order to have a .pdf copy of a quote or invoice in the email body, you must send the business email from the 'Checkout' or 'Manage' tabs from within the order.  

Because customers can have multiple orders, sending the email from inside the order is the way to make sure the appropriate quote/invoice is attached.

Here's helpful links for how and where you can email your quotes and invoices (including attachments):  How-to Email Quotes (Text)   How-to Email Quotes (Video)

   2. Some inboxes may be set to hide attachments. Your client may need to ensure that they have their inbox configured to show attachments.

Have a great day!