Hi tinfanide,
When developing automation code, it's often simpler to develop the target application's code in that application, then copy it to the automating application.
In Word, when you merge cells horizontally, only the left-most cell remains. Similarly, when you merge cells vertically, only the top-most cell remains. You can no longer address any of the other cells in the merged range. Try something based on the following Word macro:
Code:
Sub Demo()
Dim Rng As Word.Range, oDoc As Word.Document
Set oDoc = ActiveDocument
With oDoc.Tables(1)
Set Rng = .Cell(4, 2).Range
Rng.End = .Cell(6, 2).Range.End
Rng.Cells.Merge
Rng.Text = "Merged Column Cells"
End With
End Sub