C# 压缩文件文档pdf是否使用7zipsharp？

//这是我的代码压缩使用7压缩

  if (System.IO.Directory.Exists(targetfolder))
                {
                    try
                    {

                        SevenZipCompressor.SetLibraryPath(@Server.MapPath("~/bin/7z.Libs.16.2.1/bin/x64/7z.dll")); 
                        SevenZipCompressor sevenZipCompressor = new SevenZipCompressor();
                        sevenZipCompressor.CompressionLevel = SevenZip.CompressionLevel.Ultra; // level compress
                        sevenZipCompressor.CompressionMethod = CompressionMethod.Lzma2; //method compress
                        sevenZipCompressor.CompressDirectory(sourceCodeFolder, Path.Combine(targetfolder, string.Concat(DateTime.Now.ToString("ddMMyyyy_HHmm") + fldr + ".zip")));
                    }

                    catch (Exception se)
                    {
                        SevenZipCompressor.SetLibraryPath(@Server.MapPath("~/bin/7z.Libs.16.2.1/bin/x86/7z.dll"));
                        SevenZipCompressor sevenZipCompressor = new SevenZipCompressor();
                        sevenZipCompressor.CompressionLevel = SevenZip.CompressionLevel.Ultra; // level compress 
                        sevenZipCompressor.CompressionMethod = CompressionMethod.Lzma2; // method compress

//我的代码怎么了？ sevenZipCompressor.CompressDirectory（sourceCodeFolder，Path.Combine（targetfolder，string.Concat（DateTime.Now.ToString（“ddMMyyyy_HHmm”）+fldr+“.zip”）

我的问题是，为什么7zip将压缩7mb设置为仅6mb？

（大多数）PDF已经压缩，您无法通过存档获得更多信息

---

好的，谢谢，先生，我从899KB开始尝试的文档文件是715KB，是这样吗？没有一般的答案。如果您的文档文件包含大量（未压缩的）文本，则是错误的。如果有很多（已经压缩的）JPG，那么很可能没问题。

                    }


                    Directory.Delete(@Server.MapPath("~/Upload/" + fldr), true);
                    extractfrom = @Server.MapPath("~/Upload/ZIP/" + string.Concat(DateTime.Now.ToString("ddMMyyyy_HHmm")) + fldr + ".zip");

                    customSQL.ExecQueryString(" UPDATE TBL_PROGRESS_LEGAL_DOKUMEN set FileName = '" + string.Concat(DateTime.Now.ToString("ddMMyyyy_HHmm")  + namafile + ".zip"+ "'  , [FileSize] = '" + filesize + "'  where id_progress_legal_dokumen = '" + id_chekUpload.Text + "'"));
                    myfeedback._success("File Success Upload");
                }

                else
                {

                }