Locating signature with stretch mode

using (Signature signature = new Signature("sample.pdf"))
{
    // define several signature options of different types and settings
    TextSignOptions textOptions = new TextSignOptions("This is test message")
    {
        AllPages = true,
        VerticalAlignment = VerticalAlignment.Top,
        Margin = new Padding(50),
        Stretch = StretchMode.PageWidth
    };
    BarcodeSignOptions barcodeOptions = new BarcodeSignOptions("123456")
    {
        AllPages = true,
        EncodeType = BarcodeTypes.Code128,
        VerticalAlignment = VerticalAlignment.Bottom,
        Margin = new Padding(50),
        Stretch = StretchMode.PageWidth
    };
    ImageSignOptions imageOptions = new ImageSignOptions()
    {
        AllPages = true,
        Stretch = StretchMode.PageHeight,
        HorizontalAlignment = HorizontalAlignment.Right,
        ImageFilePath = Constants.ImageHandwrite
    };

    // define list of signature options
    List<SignOptions> listOptions = new List<SignOptions>();
    listOptions.Add(textOptions);
    listOptions.Add(barcodeOptions);
    listOptions.Add(imageOptions);
    // sign document to file
    signature.Sign("signed.pdf", listOptions);
}