Adding Terms and Conditions to my manually entered invoices

[sassycustomcrea]

How can I add  Terms and Conditions to my manually entered invoices?

I create a lot of custom orders where the traffic doesn't always go through out website. At checkout online customers need to click the box to indicate they accept the terms and conditions. 

Is there a way to have the terms and conditions linked to my manual invoices along with having them "sign off" on accepting.