public static void Run(
            String openPath,                            // source PDF document
            String savePath,                            // output PDF document
            String imgPath                              // watermark to apply
            )
        {
            Pdfix pdfix = PdfixEngine.Instance;

            PdfDoc doc = pdfix.OpenDoc(openPath, "");

            if (doc == null)
            {
                throw new Exception(pdfix.GetError());
            }

            // identify image format from file path
            PdfImageFormat format = PdfImageFormat.kImageFormatJpg;

            if (Path.GetExtension(imgPath).ToLower() == ".png")
            {
                format = PdfImageFormat.kImageFormatPng;
            }

            // load image file data into memory stream
            byte[] bytes  = File.ReadAllBytes(imgPath);
            var    memStm = pdfix.CreateMemStream();

            if (memStm == null)
            {
                throw new Exception(pdfix.GetError());
            }
            memStm.Write(0, bytes);

            // create XObject from the image
            var image_obj = doc.CreateXObjectFromImage(memStm, format);

            if (image_obj == null)
            {
                throw new Exception(pdfix.GetError());
            }

            // add annotation on the first page
            var page = doc.AcquirePage(0);

            if (page == null)
            {
                throw new Exception(pdfix.GetError());
            }

            var page_view = page.AcquirePageView(1, PdfRotate.kRotate0);

            if (page_view == null)
            {
                throw new Exception(pdfix.GetError());
            }

            // rect for the new annotation
            PdfRect annot_rect = new PdfRect()
            {
                left   = 100,
                right  = 300,
                bottom = 100,
                top    = 200
            };

            PdfAnnot annot = page.CreateAnnot(PdfAnnotSubtype.kAnnotStamp, annot_rect);

            page.AddAnnot(0, annot);
            // create content
            var content = doc.CreateContent();

            // add image to content
            var             xobjdict    = image_obj.GetStreamDict();
            var             width       = xobjdict.GetNumber("Width");
            var             height      = xobjdict.GetNumber("Height");
            var             ratio       = height / width;
            var             res_width   = annot_rect.right - annot_rect.left;
            var             res_height  = res_width * ratio;
            var             center_adj  = ((annot_rect.top - annot_rect.bottom) - res_height) / 2;
            var             imageobject = content.AddNewImage(-1, image_obj, new PdfMatrix(res_width, 0, 0, res_height, 0, center_adj));
            PdfGraphicState imageGs     = new PdfGraphicState();

            imageGs.color_state.fill_opacity = 255;
            imageobject.SetGState(imageGs);

            // create text state
            PdfTextState textState  = new PdfTextState();
            var          colorSpace = doc.CreateColorSpace(PdfColorSpaceFamily.kColorSpaceDeviceRGB);
            var          fontName   = "Segoe UI";
            var          fn         = fontName.Trim();
            var          sysFont    = pdfix.FindSysFont(fn, 0, PdfFontCodepage.kFontDefANSICodepage);

            if (sysFont == null)
            {
                throw new Exception(pdfix.GetError());
            }
            textState.font = doc.CreateFont(sysFont, PdfFontCharset.kFontAnsiCharset, 0);
            sysFont.Destroy();

            if (textState.font == null)
            {
                throw new Exception(pdfix.GetError());
            }

            textState.font_size             = 11;
            textState.color_state.fill_type = PdfFillType.kFillTypeSolid;
            var fill_color = colorSpace.CreateColor();

            fill_color.SetValue(0, 0.5f);
            fill_color.SetValue(1, 0.5f);
            fill_color.SetValue(2, 0.5f);
            textState.color_state.fill_color   = fill_color;
            textState.color_state.fill_opacity = 255;
            textState.color_state.stroke_type  = PdfFillType.kFillTypeSolid;
            var stroke_color = colorSpace.CreateColor();

            stroke_color.SetValue(0, 0);
            stroke_color.SetValue(1, 0);
            stroke_color.SetValue(2, 0);
            textState.color_state.stroke_color   = stroke_color;
            textState.color_state.stroke_opacity = 255;
            textState.char_spacing = 2;

            // add text to content
            var line       = "test text in appearance";
            var textObject = content.AddNewText(-1, textState.font, new PdfMatrix(1, 0, 0, 1, 10, 10));

            if (textObject == null)
            {
                throw new Exception(pdfix.GetError());
            }

            textObject.SetTextState(textState);
            textObject.SetText(line);

            // set annotation appearance
            PdsContentParams contentParams = new PdsContentParams();

            contentParams.bbox      = new PdfRect(annot_rect.right - annot_rect.left, 0, 0, annot_rect.top - annot_rect.bottom);
            contentParams.matrix    = new PdfMatrix(1, 0, 0, 1, 0, 0);
            contentParams.form_type = 1;
            contentParams.flags     = 2;
            var appearance_stream = content.ToObject(doc, contentParams);

            annot.SetAppearanceFromXObject(appearance_stream, PdfAnnotAppearanceMode.kAppearanceNormal);

            page.Release();

            // save document
            if (!doc.Save(savePath, Pdfix.kSaveFull))
            {
                throw new Exception(pdfix.GetError());
            }

            doc.Close();
        }