public override DocumentPage GetPage(int numPage)
{
DrawingVisual vis = new DrawingVisual();
DrawingContext dc = vis.RenderOpen();
double factor = Math.Min((PageSize.Width-96)/sizeMax.Width, (PageSize.Height-96)/sizeMax.Height);
FormattedText formtxt = GetFormattedText(txt[numPage], face, factor*100);
Point ptText = new Point((PageSize.Width - formtxt.Width)/2, (PageSize.Height - formtxt.Height)/2);
dc.DrawText(formtxt, ptText);
dc.Close();
return new DocumentPage(vis);
}