Text Box on the Template is meant for Fixed Text, like a Preprinted form with a Permanent message on it.

It is not meant for Freeform Text entries, while you work.

This is not a Word Processing program. This is your Financial data management program.

You can add details to an Item's description line, up to 4,095 characters, but you want to avoid a lot of typing. For instance, contract agreement terms would be a separate document, not part of an Order document.