Thai letters not rendering properly

Question

I'm using pechkin.dll for convert HTML to PDF but thai characters are rendering improperly.

 

Sample - ???????????? this word after convert showing as ?????????? ?#?(Thai fonts not displaying)

 

//SAMPLE CODE string html; html = html.Replace("Brnch", WebUtility.HtmlEncode("????????????"));

var pdf = pechkin.Convert(new ObjectConfig() .SetLoadImages(true) .SetZoomFactor(1) .SetPrintBackground(true) .SetScreenMediaType(true) .SetCreateExternalLinks(true) .SetIntelligentShrinking(true) .SetCreateInternalLinks(true) .SetCreateForms(true), System.Text.Encoding.UTF8.GetBytes(strHTML));