How to draw different font style in the same line of PDF in WinRT?

float nextText = 0;
private void Button_Click(object sender, RoutedEventArgs e)
{
    // Creates a new PDF document
    PdfDocument doc = new PdfDocument();
    // Add a page
    PdfPage page = doc.Pages.Add();
    // Create PDF graphics for the page
    PdfGraphics g = page.Graphics;
    PdfBrush brush = PdfBrushes.Black;
    PdfFont boldFont = new PdfStandardFont(PdfFontFamily.TimesRoman, 12, PdfFontStyle.Bold);
    PdfFont regularFont = new PdfStandardFont(PdfFontFamily.TimesRoman, 12, PdfFontStyle.Regular);
    PdfFont italicFont = new PdfStandardFont(PdfFontFamily.TimesRoman, 12, PdfFontStyle.Italic);
    PdfLayoutResult result;
    result = AddString("Hello World ", page, 0, brush, boldFont);
    result = AddString("Hello World ", page, result.Bounds.Width, brush, regularFont);
    result = AddString("Hello World ", page, result.Bounds.Width, brush, italicFont);
}
private PdfLayoutResult AddString(string note, PdfPage newPage, float xPosition, PdfBrush brush, PdfFont font)
{
    float SpacValue = 10.0f;
    nextText = nextText + (xPosition + SpacValue);
    // Rendering Text
    PdfTextElement richTextElement = new PdfTextElement(note, font, brush);
    // Draws String
    PdfLayoutResult result = richTextElement.Draw(newPage, new RectangleF(nextText, 0, 0, 0));
    return result;
}