Private _boundingArea As System.Drawing.RectangleF
Private _annotation As Vintasoft.Imaging.Annotation.AnnotationData

Private Sub SubscribeOnPropertyChanging()
    AddHandler _annotation.PropertyChanging, New System.EventHandler(Of Vintasoft.Imaging.ObjectPropertyChangingEventArgs)(AddressOf annotation_PropertyChanging)
End Sub

Private Sub annotation_PropertyChanging(sender As Object, e As Vintasoft.Imaging.ObjectPropertyChangingEventArgs)
    If e.PropertyName = "Rotation" Then
        Dim boundingBox As System.Drawing.RectangleF = _annotation.GetBoundingBox(_annotation.Location, _annotation.Size, CSng(e.NewValue))

        If Not _boundingArea.Contains(boundingBox) Then
            e.Cancel = True
        End If
    End If
End Sub

System.Drawing.RectangleF _boundingArea;
Vintasoft.Imaging.Annotation.AnnotationData _annotation;

void SubscribeOnPropertyChanging()
{
    _annotation.PropertyChanging += 
        new System.EventHandler<Vintasoft.Imaging.ObjectPropertyChangingEventArgs>(annotation_PropertyChanging);
}

void annotation_PropertyChanging(object sender, Vintasoft.Imaging.ObjectPropertyChangingEventArgs e)
{
    if (e.PropertyName == "Rotation")
    {
        System.Drawing.RectangleF boundingBox = _annotation.GetBoundingBox(
            _annotation.Location, _annotation.Size, (float)e.NewValue);

        if (!_boundingArea.Contains(boundingBox))
        {
            e.Cancel = true;
        }
    }
}