A link to the order doesn't work for us too. The email that is being sent to the customers should only contain a PDF document and no links to the order. This way you actually have a document. The problem is that if somebody of my employees makes a change to the order status for example, before the customer has opened the link and downloaded the PDF, the link leads you to the new order status. Here is an example from yesterday:
Since we are in the EU we often have to issue proforma invoices, which allow our customers to pay in advance for the goods. TG does not have a feature for creating proforma invoices and therefore I made a little workaround, by simply changing the Sales Quote name in templates to Proforma Invoice. However, yesterday I had to send a proforma to the customer and immediately ship the goods. What happened is that I emailed the proforma, while the order was saved as quote and then approved it in order to ship the goods. The customer opened the email with topic "Proforma Invoice" and saw a "Sales Order" in the link inside.
I had to delete everything and restart the process.