Some templates contain data sources.
A data sources is a linked file that columns and rows of data. The columns populate merge codes to create multiple letters from a single source.
An example of a data source is a list of creditors. One of the data fields may be called “CompanyName” for example. The document template may have a merge code called «CompanyName» allowing you to create multiple documents as the output producing a separate personalised letter as the output.
When inserting a data field make sure you can right click on the field and the "Edit Field" option is available.
If you don't have the option to insert a «Mergefield», one option is to copy an existing field, then edit it's properties, to add a different data field.
This shows the edited field:
A list of available merge fields for each data source are shown in the Merge Field Listing available from the Manage Document Templates reports.
A data source is applied to a template by selecting the "This datasource:" option when configuring the template.