In the quotation and invoice message you can manually add extra attachments to the e-mail message.
You can include your general terms and conditions in the quotation. These can be uploaded via setup > settings > company details.
Please note that the more information you add to an e-mail, the longer it will take for it to be sent. This increases the chance that the e-mail does not arrive in full as certain security checks can be set to only receive a certain maximum file size.
It is therefore not possible to add an attachment to a standard message. However, you can share this information by adding a link to the message.
Do this by selecting the text and clicking on the 'link' icon, after which you can insert the link.
A link to a document
You can put a document online, for example, by placing it on your website domain or by sharing it publicly in, for example, Google drive.
Learn more about sharing files from Google Drive
A link to a page on your website
For information such as a route description it is advisable to put this on your website and to put a link to the correct page in the (automatic) message. This way, information stays up-to-date by adjusting it on your page.