Add TextBox

This macro will add a TextBox to the active Word document:

Sub AddTextBox()
ActiveDocument.Shapes.AddTextBox Orientation:=msoTextOrientationHorizontal, Left:=1, Top:=1, Width:=300, Height:=100
End Sub

Delete TextBox

This VBA macro will delete the first TextBox in the active document:

Sub DeleteTextBox()
'deletes first text box in activedoc
'not straithforward because its not easy to identify text boxes
    Dim oShape As Shape
    If ActiveDocument.Shapes.Count > 0 Then
        For Each oShape In ActiveDocument.Shapes
            If oShape.AutoShapeType = msoShapeRectangle Then 'we need to check both if oShape is of type msoShapeRectangle and its textframe contains place for writing
                If oShape.TextFrame.HasText = True Then
                    oShape.Delete
                End If
            End If
        Next oShape
    End If
End Sub
AutoMacro - VBA Code Generator

Write in TextBox

This Word macro uses similar methodology to write to the first TextBox in the active document:

Sub WriteInTextBox()
'writes into first text box in active doc
Dim oShape As Shape
    If ActiveDocument.Shapes.Count > 0 Then
        For Each oShape In ActiveDocument.Shapes
            If oShape.AutoShapeType = msoShapeRectangle Then 'we need to check both if oShape is of type msoShapeRectangle and its textframe contains place for writing
                If oShape.TextFrame.HasText = True Then
                    oShape.TextFrame.TextRange.InsertAfter "https://www.automateexcel.com/vba-code-library"
                    Exit For 'we just want to write into first textbox
                End If
            End If
        Next oShape
    End If
End Sub