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;
 }