OpenHeaderSource Method Example
This example sets the active document as a main document for form letters, and then it attaches the header source named "Header.doc" and the data document named "Names.doc."
With ActiveDocument.MailMerge
.MainDocumentType = wdFormLetters
.OpenHeaderSource Name:="C:\My Documents\Header.doc", _
Revert:=False, AddToRecentFiles:=False
.OpenDataSource Name:="C:\My Documents\Names.doc"
End With