You have the option to attach the built-in receipt/invoice to all emails, but you can also attach additional documents if you wish. You may want to add a PDF document with directions to your property/site or perhaps you’d like to send out some information about things to do in the area.
All you need to do is create your document and save it as a PDF (this means that it will be read only rather than editable). To add your attachment check the attach additional attachment box on the email page. A box will appear saying click to upload attachment. This will allow you to choose from the files on your computer.
Once you have uploaded your document you need to press the save button at the bottom of the page.