.Net5 WebApi中操作PDF（分割复制PDF指定页 and 合并多个PDF文件）

• 安装Nuget包
• PDF工具类 and 合并多个PDF为一个PDF

安装Nuget包

.Net Framework：install-package iTextSharp

.Net Core/.Net5：install-package iTextSharp.LGPLv2.Core（我安装的1.7.1）

PDF工具类 and 合并多个PDF为一个PDF

using iTextSharp.text;
using iTextSharp.text.pdf;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Levox.Framework.Core.CommonUtils;
using Levox.Framework.Core.Extensions;
using Levox.Framework.Core.Models.Exceptions;
using Levox.Framework.Core.Models.File;

namespace Levox.Framework.Core.Pdfs
{
    public class PdfUtil
    {
        /// <summary>
        /// 复制目标PDF文件的指定页内容，生成一个新的PDF文件   LastUpdateDate：2021-06-29 14:36:33.875  Author：Lingbug
        /// </summary>
        /// <param name="outputPdfFileName">新PDF文件名（自动识别是否带有.pdf后缀），为空默认为OutputSplitPdfFileName</param>
        /// <param name="sourcePdfPath">目标PDF文件在系统内的相对路径</param>
        /// <param name="pageNumbers">要复制的页集合，从1开始</param>
        /// <returns>新的PDF文件相对路径</returns>
        public static string CreatePdfByCustomPages(string outputPdfFileName, string sourcePdfPath, IEnumerable<int> pageNumbers)
        {
            //校验
            if (sourcePdfPath.IsNullOrWhiteSpaceString()) throw new ErpFriendlyException("要分割复制的PDF源文件路径不能为空！");
            //校验
            if (pageNumbers.IsNullOrEmptyList()) throw new ErpFriendlyException("要复制的PDF页码集合不能为空！");
            //去重排序
            pageNumbers = pageNumbers.Distinct().OrderBy(r => r);
            //校验
            if (pageNumbers.First() <= 0) throw new ErpFriendlyException("要复制的PDF页码必须大于0！");

            //完整路径
            string sourcePdfFullPath = FileUtil.GetFullPath(sourcePdfPath);
            //校验
            if (!File.Exists(sourcePdfFullPath)) throw new ErpFriendlyException("要复制分割的PDF源文件不存在！");

            //读取源文件
            var reader = new PdfReader(sourcePdfFullPath);
            //校验
            if (pageNumbers.Last() > reader.NumberOfPages) throw new ErpFriendlyException($"要复制的PDF页码必须小于等于源文件总页数【{reader.NumberOfPages}】！");

            //结果文件
            var fileOutput = GetOutputPdfFileInfo(outputPdfFileName, "OutputSplitPdfFileName");

            //初始化
            var sourceDocument = new Document(reader.GetPageSizeWithRotation(pageNumbers.First()));
            //初始化
            var pdfCopyProvider = new PdfCopy(sourceDocument, new FileStream(fileOutput.FileFullPath, FileMode.Create));
            //打开
            sourceDocument.Open();

            //复制指定页
            foreach (var pageNumber in pageNumbers) pdfCopyProvider.AddPage(pdfCopyProvider.GetImportedPage(reader, pageNumber));

            //关闭
            sourceDocument.Close();
            //关闭
            reader.Close();

            //返回
            return fileOutput.FilePath;
        }

        /// <summary>
        /// 将多个PDF文件合并为一个PDF文件   LastUpdateDate：2021-06-29 16:23:23.438  Author：Lingbug
        /// </summary>
        /// <param name="outputPdfFileName">新PDF文件名（自动识别是否带有.pdf后缀），为空默认为OutputMergePdfFileName</param>
        /// <param name="sourcePdfPathList">要合并的源PDF文件相对路径集合</param>
        /// <returns>新的PDF文件相对路径</returns>
        public static string MergePdfs(string outputPdfFileName, params string[] sourcePdfPathList)
        {
            //校验
            if (sourcePdfPathList.IsNullOrEmptyList()) throw new ErpFriendlyException("要合并的PDF相对路径集合不能为空！");
            //过滤
            sourcePdfPathList = sourcePdfPathList.Where(r => !r.IsNullOrWhiteSpaceString()).Distinct().ToArray();
            //校验
            if (sourcePdfPathList.IsNullOrEmptyList()) throw new ErpFriendlyException("要合并的PDF相对路径集合不能为空！");

            //获取完整路径
            var sourcePdfFullPathList = sourcePdfPathList.Select(sourcePdfPath =>
            {
                //完整路径
                string sourcePdfFullPath = FileUtil.GetFullPath(sourcePdfPath);
                //校验
                if (!File.Exists(sourcePdfFullPath)) throw new ErpFriendlyException("要合并的PDF源文件不存在：" + sourcePdfPath);
                //返回
                return sourcePdfFullPath;
            }).ToArray();

            //结果文件
            var fileOutput = GetOutputPdfFileInfo(outputPdfFileName, "OutputMergePdfFileName");

            //读取器
            PdfReader reader;
            //文档
            Document doc = new Document();
            //写入器
            PdfWriter writer = PdfWriter.GetInstance(doc, new FileStream(fileOutput.FileFullPath, FileMode.Create));
            //打开文档
            doc.Open();
            //内容容器
            PdfContentByte cb = writer.DirectContent;
            //页
            PdfImportedPage newPage;
            for (int i = 0; i < sourcePdfFullPathList.Length; i++)
            {
                //读取文件
                reader = new PdfReader(sourcePdfFullPathList[i]);
                //总页数
                int totalPages = reader.NumberOfPages;
                for (int j = 1; j <= totalPages; j++)
                {
                    //读取页
                    newPage = writer.GetImportedPage(reader, j);
                    //页大小
                    doc.SetPageSize(reader.GetPageSize(j));
                    //开启新页
                    doc.NewPage();
                    //填充内容
                    cb.AddTemplate(newPage, 0, 0);
                }
            }
            //关闭文档
            doc.Close();
            //返回
            return fileOutput.FilePath;
        }

        /// <summary>
        /// 构建输出PDF文件信息   LastUpdateDate：2021-06-29 16:14:28.454  Author：Lingbug
        /// </summary>
        /// <param name="outputPdfFileName"></param>
        /// <param name="defaultOutputPdfFileName"></param>
        /// <returns></returns>
        private static SaveFileOutput GetOutputPdfFileInfo(string outputPdfFileName, string defaultOutputPdfFileName)
        {
            //默认名称
            if (outputPdfFileName.IsNullOrWhiteSpaceString()) outputPdfFileName = defaultOutputPdfFileName;
            //格式化
            outputPdfFileName = outputPdfFileName.AutoAppendEnd(".pdf");
            //结果文件
            return new SaveFileOutput(outputPdfFileName, "UploadFiles", "Temp", "Pdfs");
        }
    }
}