var pp = new PDFConvert();
pp.OutputFormat = "jpeg"; //format
pp.JPEGQuality = 90; //100% quality
pp.ResolutionX = 120; //dpi
pp.ResolutionY = 120;
pp.FirstPageToConvert = 1; //pages you want
pp.LastPageToConvert = 1;
pp.Convert(Server.MapPath("~/Pdf Files/20.pdf"), Server.MapPath("~/pdf/") + "1.jpg");