The FRS Tools plug-in exposes a set of fields which can be used to create document templates in ContactsLaw. These fields will only yield data when documents are created via the 'generate documents' function on the FRS mailout activity.
To create a template which draws upon these fields, tick 'FRS mailout fields' on the Fields tab of the document template editor in ContactsLaw. They will appear under the 'FRSProperty' node. Fields in this group will return at most a single result for the property to which the document pertains. You can also access fields on the contact linked to the property (if present).
For further information, refer to the documentation displayed for each field as you select it in the editor.