This example displays the name of each field in the data source attached to the active mail merge main document.
For Each mField In ActiveDocument.MailMerge.DataSource.DataFields
MsgBox mField.Name
Next mField
This example displays the value of the LastName field from the first record in the data source attached to "Main.doc."
With Documents("Main.doc").MailMerge.DataSource
.ActiveRecord = wdFirstRecord
MsgBox .DataFields("LastName").Value
End With