Private wdApp As Word.Application

Sub MergeCells()

    Dim wdDoc As Word.Document
    Dim wdTbl As Word.Table
     
    Set wdApp = New Word.Application
    
    Set wdDoc = wdApp.Documents.Open(Filename:="D:\1\Test.doc")
    Set wdTbl = wdDoc.Tables( 1 )
    
    wdTbl.Cell( 1 ,  1 ).Select
    wdApp.Selection.MoveDown wdLine,  1 , wdExtend
    wdApp.Selection.Cells.Merge
End Sub

Sub AppVisible()

    wdApp.Visible = True
End Sub

    With wdTbl
        .Cell(Row:= 1 , Column:= 1 ).Merge _
            MergeTo:=.Cell(Row:= 2 , Column:= 1 )
        .Borders.Enable = True
    End With