This tip demonstrates how to attach the DB source and populate fields from table to a mail merged word document in VB.NET.
Code Snippet

Dim objWord As New Object
objWord = CreateObject("Word.Application") ' Creating a word application
 
Dim objDoc As New Object
objDoc = CreateObject("Word.Document") ' Creating a word document object
 
objWord.application.WindowState = 0 ' set the word window in normal state (Const wdWindowStateNormal = 0)
objDoc = objWord.Documents.Add(DocsFolder.FullName & "\YOUR WORD DOC NAME") ' Add the mail merged document file
 
Dim NameBeforeWordMerge As String = objWord.ActiveDocument.Name
 
objWord.ActiveDocument.MailMerge.OpenDataSource("YOUR DATABASE PATH", _
               Connection:="dsn=DSN NAME; dbq=" & YOUR DATABASE PATH & ";", _
               sqlstatement:="select * from `" & tableName & "`")
 
With objWord.ActiveDocument.MailMerge
         .MailAsAttachment = False
         .MailAddressFieldName = ""
         .MailSubject = ""
        .SuppressBlankLines = True
         With .DataSource
               .FirstRecord = 1  ' Const wdDefaultFirstRecord = 1
               .LastRecord = -16 ' Const wdDefaultLastRecord = -16 (&HFFFFFFF0)
         End With
        .Execute(pause:=True)
End With
      
 Dim NameAfterWordMerge As String = objWord.ActiveDocument.Name
 
objWord.Documents(NameBeforeWordMerge ).Close(0) ' close the template doc
objWord.Documents(NameAfterWordMerge ).Activate() ' activate the mail merged doc after record population

And you are done …