private void Form2_EditorInitialized(object sender, RadPageViewEditorEventArgs e)
{
    var editor = (this.radPageView1.ViewElement as RadPageViewStripElement).ActiveEditor as PageViewItemTextEditor;
    editor.ValueChanged += Editor_ValueChanged;
    var element = editor.EditorElement as PageViewItemTextEditorElement;
    element.TextChanged += Element_TextChanged;
}

private void Element_TextChanged(object sender, EventArgs e)
{
    var element = sender as PageViewItemTextEditorElement;
    string text = element.Text;
    var textSize = TextBoxControlMeasurer.MeasureText(text, element.Font);
    element.MinSize = new Size(textSize.Width + 4, 0);

    element.Parent.MinSize = new Size(textSize.Width + 20, 0);
}