C# 给PDF添加文字水印_c# pdf添加水印-优快云博客

该代码示例展示了如何使用iTextSharp库在PDF文档上添加文字水印，包括设置水印的透明度、位置以及是否显示在内容上方或下方。

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安装iTextSharp

        /// <summary>
        /// PDF添加文字水印
        /// </summary>
        /// <param name="source"></param>
        /// <param name="waterMark">水印文字内容</param>
        /// <param name="markOpacity">水印透明度，默认0.15f</param>
        /// <param name="waterMark">水印在文字上方或下方：上方1；其它下方</param>
        /// <returns></returns>
        public static byte[] SetPDFWaterMark(byte[] source, string waterMark, float markOpacity = 0.15f, int OverContent = 1)
        {
            byte[] rtnContent = null;
            PdfReader pdfReader = null;
            PdfStamper pdfStamper = null;
            try
            {
                pdfReader = new PdfReader(source);

                using (MemoryStream stream = BytesToMemoryStream(source))
                {
                    pdfStamper = new PdfStamper(pdfReader, stream);
                    int total = pdfReader.NumberOfPages + 1;
                    iTextSharp.text.Rectangle psize = pdfReader.GetPageSize(1);
                    float width = psize.Width;
                    float height = psize.Height;
                    PdfContentByte content;
                    BaseFont font = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.WINANSI, BaseFont.NOT_EMBEDDED);
                    PdfGState gs = new PdfGState();
                    for (int i = 1; i < total; i++)
                    {
                        //content = pdfStamper.GetOverContent(i);//在内容上方加水印
                        //content = pdfStamper.GetUnderContent(i);//在内容下方加水印
                        content = OverContent == 1 ? pdfStamper.GetOverContent(i) : pdfStamper.GetUnderContent(i);

                        //透明度
                        gs.FillOpacity = markOpacity;
                        content.SetGState(gs);
                        for (int j = 1; j <= 4; j++)
                        {
                            //开始写入水印文本
                            content.BeginText();
                            content.SetColorFill(iTextSharp.text.BaseColor.GRAY);
                            content.SetFontAndSize(font, 30);
                            content.SetTextMatrix(0, 0);
                            content.ShowTextAligned(iTextSharp.text.Element.ALIGN_CENTER, waterMark, width - 120 * j, height - 120 * j, -30);
                            content.EndText();
                        }

                    }
                    pdfStamper.Close();
                    rtnContent = stream.ToArray();
                }

            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                if (pdfReader != null)
                    pdfReader.Close();
            }
            return rtnContent;
        }

        public static MemoryStream BytesToMemoryStream(byte[] source)
        {
            var ms = new MemoryStream();
            int read;
            while ((read = ms.Read(source, 0, source.Length)) > 0)
            {
                ms.Write(source, 0, read);
            }
            return ms;

        }