How to Prepare Rich Text Content for Templates
X-Author templates only support Rich Text content developed using the Rich Text editor in Salesforce. RTA fields inside templates generate field content exactly as shown on the agreement record. Before generating an agreement based on a template containing RTA fields, edit the agreement record directly to format your Rich Text content.
Be aware that copy-paste or data loading of Rich Text content that includes formatting not available using the editor (e.g., tables) may or may not appear correctly in generated documents. Refer to Salesforce documentation for HTML limitations if attempting to include RTF content in this way.