MailMergeDataSource.DataFields (Word)
Returns a MailMergeDataFields collection that represents the fields in the specified mail merge data source.
For information about returning a single member of a collection, see Returning an object from a collection.
Dim mmdfTemp As MailMergeDataField
For Each mmdfTemp In _
ActiveDocument.MailMerge.DataSource.DataFields
MsgBox mmdfTemp.Name
Next mmdfTemp