PdfDocument pdf = new PdfDocument();
 PdfPageBase page = pdf.Pages.Add();
 PdfRGBColor c = Color.Purple;

 //color space RGB
 PdfSeparationColorSpace cs = new PdfSeparationColorSpace("MySpotColor", new PdfRGBColor(c.R, c.G, c.B));
 //color space CMYK
 PdfSeparationColorSpace cs = new PdfSeparationColorSpace("MySpotColor", new PdfRGBColor(c.C, c.M, c.Y, c.K));
 //color space Grayscale
 PdfSeparationColorSpace cs = new PdfSeparationColorSpace("MySpotColor", new PdfRGBColor(c.Gray));

 PdfSeparationColor color = new PdfSeparationColor(cs, 1f);
 PdfSolidBrush brush = new PdfSolidBrush(color);
 page.Canvas.DrawPie(brush, 10, 30, 60, 60, 360, 360);
 page.Canvas.DrawString("Tint=1.0", new PdfFont(PdfFontFamily.Helvetica, 10f), brush, new PointF(22, 100));
 color = new PdfSeparationColor(cs, 0.5f);
 brush = new PdfSolidBrush(color);
 page.Canvas.DrawPie(brush, 80, 30, 60, 60, 360, 360);
 page.Canvas.DrawString("Tint=0.5", new PdfFont(PdfFontFamily.Helvetica, 10f), brush, new PointF(92, 100));
 color = new PdfSeparationColor(cs, 0.25f);
 brush = new PdfSolidBrush(color);
 page.Canvas.DrawPie(brush, 150, 30, 60, 60, 360, 360);
 page.Canvas.DrawString("Tint=0.25", new PdfFont(PdfFontFamily.Helvetica, 10f), brush, new PointF(162, 100));
 pdf.SaveToFile("SpotColorrgb.pdf");

PdfCompressor compressor = new PdfCompressor(fileName);
compressor.Options.TextCompressionOptions.UnembedFonts = true;
compressor.CompressToFIle(outputName);