Private Sub CheckBox1_Click()
Dim oRng As Range
Dim oFld As Field
    If CheckBox1.Value = True Then
        Set oRng = Selection.Range
        oRng.End = oRng.End + 1
        oRng.Collapse 0
        oRng.Text = Format(Date, "dd/MM/yyyy ") & Format(Time, "hh:mm")
        oRng.Collapse 0
        oRng.Text = ", "
        oRng.Collapse 0
        Set oFld = oRng.Fields.Add(Range:=oRng, Type:=wdFieldUserName, PreserveFormatting:=False)
        oRng.End = oFld.Result.End
        oRng.Collapse 0
        oRng.Text = vbCr
        oRng.Collapse 0
    End If
 End Sub

Private Sub CheckBox1_Click()
Dim oRng As Range
Dim bCC As Boolean
Dim oCC As ContentControl
Dim sTime As String
    For Each oCC In ActiveDocument.ContentControls
        If oCC.Title = "Completed" Then bCC = True
        Exit For
    Next oCC
    If CheckBox1.Value = True Then
        sTime = Format(Date, "dd/MM/yyyy ") & Format(Time, "hh:mm") & ", " & Application.UserName
        If bCC = True Then
            oCC.LockContents = False
            oCC.Range.Text = sTime
            oCC.LockContents = True
        Else
            Set oRng = Selection.Range
            oRng.End = oRng.End + 1
            oRng.Collapse 0
            Set oCC = oRng.ContentControls.Add
            With oCC
                .Type = wdContentControlRichText
                .Title = "Completed"
                .Tag = .Title
                .Range.Text = sTime
                .LockContentControl = True
                .LockContents = True
            End With
            Set oRng = oCC.Range
            oRng.End = oRng.End + 1
            oRng.Collapse 0
            oRng.InsertParagraph
        End If
    Else
        If bCC = True Then
            oCC.LockContents = False
            oCC.Range.Text = ChrW(8203)
            oCC.LockContents = True
        End If
    End If
    Set oCC = Nothing
    Set oRng = Nothing
End Sub