Aspose - Issue with TextBoxField

public byte[] AddTextBoxToPdfFile(byte[] currentPDF, SignatureInformation signature)
{
    Aspose.Pdf.Document document = new Aspose.Pdf.Document(new MemoryStream(currentPDF));
    TextFragmentAbsorber textFragmentAbsorber = new TextFragmentAbsorber(signature.IdCase);
    documentPdf.Pages.Accept(textFragmentAbsorber);

    TextFragmentCollection initialCollection = textFragmentAbsorber.TextFragments;
    if (initialCollection.Count <= 0) return currentPDF;
    TextFragment fragment = initialCollection[1];

    var signatureRectangle = SetupDefaultSignatureRectangle(fragment);
    var textBoxField = new TextBoxField(documentPdf, signatureRectangle)
    {
        PartialName = signature.IdCase
    };
    documentPdf.Form.Add(textBoxField, fragment.Page.Number);

    var rectangleForSignerName = CreateRectangleUnder(signatureRectangle);
    var signerBoxField = new TextBoxField(documentPdf, rectangleForSignerName)
    {
        PartialName = signature.IdSignatureCase
    };
    documentPdf.Form.Add(signerBoxField, fragment.Page.Number);

    var rectangleForDate = CreateRectangleUnder(rectangleForSignerName);
    var dateField = new TextBoxField(documentPdf, rectangleForDate)
    {
        PartialName = signature.IdDateCase
    };
    documentPdf.Form.Add(dateField, fragment.Page.Number);

    var turin = Path.GetTempFileName() + EXTENSION_PDF;
    documentPdf.Save(turin);

    return File.ReadAllBytes(turin);
}

private Rectangle SetupDefaultSignatureRectangle(TextFragment fragment)
{
    return new Rectangle(
        fragment.Position.XIndent,
        fragment.Position.YIndent + 25,
        UPPER_RIGHT_X,
        fragment.Position.YIndent - 100);
}

private Rectangle CreateRectangleUnder(Rectangle upperRectangle)
{
    return new Rectangle(
        upperRectangle.LLX,
        upperRectangle.LLY - MARGIN,
        UPPER_RIGHT_X,
        upperRectangle.LLY - MARGIN - 15);
}