c# 修改pdf

继续引用spire的dll。

1.代码如下：

PdfDocument doc = new PdfDocument();
            doc.LoadFromFile("wen.pdf");
            PdfPageBase page = doc.Pages[doc.Pages.Count-1];
            System.Drawing.Font font = new System.Drawing.Font("微软雅黑", 9, FontStyle.Regular);
            PdfTrueTypeFont trueTypeFont = new PdfTrueTypeFont(font, true);
            page.Canvas.DrawString("请在此输入建议：", trueTypeFont, new PdfSolidBrush(Color.Black), 80, 180);
            doc.SaveToFile("MyFirstPDF.pdf");
            //page.Canvas.DrawString("请在此输入建议：",
            //new PdfFont(PdfFontFamily.Helvetica, 9f),
            //new PdfSolidBrush(Color.Black), 80, 180);
            //doc.SaveToFile("MyFirstPDF.pdf");//如果用此中文乱码
            doc.Close();

 2.进阶：

　　问题情境：要修改的地方原先就有东西，需要删除再覆盖：

　　解决办法：先添加白色brush矩形覆盖，再进行添加内容

PdfDocument doc = new PdfDocument();
                doc.LoadFromFile("orignal.pdf");
                PdfPageBase page = doc.Pages[doc.Pages.Count - 1];
                RectangleF rectangle = new RectangleF(80,180,500,500);
                PdfBrush brush = PdfBrushes.White;
                page.Canvas.DrawRectangle(brush, rectangle);


                System.Drawing.Font font = new System.Drawing.Font("微软雅黑", 12, FontStyle.Regular, GraphicsUnit.World);
                PdfTrueTypeFont trueTypeFont = new PdfTrueTypeFont(font, true);
                page.Canvas.DrawString(editStr, trueTypeFont, new PdfSolidBrush(Color.Black), 80, 180);
                doc.SaveToFile("now.pdf");
                doc.Close();

3.后加textBox获取换行符

private string getEditString(string strOrig)
        {
            int numL = 40;
            string editStr = strOrig;
            string[] strs = editStr.Split(new string[1] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
            editStr = "";

            for (int i = 0; i < strs.Length; i++)
            {
                float numC = 0F;

                int addT = 0;
                for (int k = 0; k < strs[i].Length; k++)
                {
                    try
                    {
                        if (!Regex.IsMatch(strs[i].Substring(k, 1), @"[a-zA-Z0-9]"))
                        {
                            numC += 1;
                        }
                        else
                        {
                            numC += 0.5f;
                            addT++;
                        }
                        if (numC > numL)
                        {
                            break;
                        }
                    }
                    catch(Exception eeee)
                    {
                        throw eeee;
                    }
                }
                if (numC > numL)
                {
                    string str = strs[i].Insert(numL - 1 + addT / 2, "\r\n");
                    editStr += getEditString(str);
                    continue;
                }
                else
                {
                    editStr += strs[i] + "\r\n";
                }
            }
            return editStr;
        }

 附加：

　　1.行间距设置：PdfStringFormat stringFormat = new PdfStringFormat();
            stringFormat.LineSpacing = 16f;