基于C#实现PDF按页分割文件和分页合并

using iTextSharp.text;
using iTextSharp.text.pdf;

// 目标分割pdf文件
string inputFilePath = @"你自己的pdf文件物理路径.pdf";

// 创建输出文件所在文件夹
string outputFolder = "NewFile";
string rootPath = System.IO.Directory.GetCurrentDirectory();
string folderAll = Path.Combine(rootPath, outputFolder);
if (!Directory.Exists(folderAll))
{
    Directory.CreateDirectory(folderAll);
}

// 操作pdf分割
using (PdfReader reader = new PdfReader(inputFilePath))
{
    for (int i = 1; i <= reader.NumberOfPages; i++)
    {
        string newFilePath = Path.Combine(outputFolder, $"page_{i}.pdf");
        
        using (Document document = new Document())
        using (PdfCopy copy = new PdfCopy(document, new FileStream(newFilePath, FileMode.Create)))
        {
            document.Open();
            copy.AddPage(copy.GetImportedPage(reader, i));
            document.Close();
        }
    }
}

Console.WriteLine("PDF 分割完成！");

// 目标合并pdf文件
string[] sourceFiles = new string[] {
    @"你的pdf文件1.pdf",
    @"你的pdf文件2.pdf"
};

// 创建输出文件所在文件夹
string outputFolder = "NewFile";
string rootPath = System.IO.Directory.GetCurrentDirectory();
string folderAll = Path.Combine(rootPath, outputFolder);
if (!Directory.Exists(folderAll))
{
    Directory.CreateDirectory(folderAll);
}

using (Document document = new Document())
{
    PdfCopy copy = new PdfCopy(document, new FileStream($"{outputFolder}\\page_1_20_Add_21_40.pdf", FileMode.Create));
    document.Open();

    foreach (string file in sourceFiles)
    {
        using (PdfReader reader = new PdfReader(file))
        {
            for (int i = 1; i <= reader.NumberOfPages; i++)
            {
                copy.AddPage(copy.GetImportedPage(reader, i));
            }
        }
    }

    document.Close();
    copy.Close();
}

    // 目标分割pdf文件
    string inputFilePath = @"你自己的pdf文件物理路径.pdf";

    // 创建输出文件所在文件夹
    string outputFolder = "NewFile";
    string rootPath = System.IO.Directory.GetCurrentDirectory();
    string folderAll = Path.Combine(rootPath, outputFolder);
    if (!Directory.Exists(folderAll))
    {
        Directory.CreateDirectory(folderAll);
    }

    // 操作pdf分割
    using (PdfReader reader = new PdfReader(inputFilePath))
    {
        int startPage = 1;
        int pageSize = 0;
        int totalPage = 0;
        int unitSize = 20;
        int remainder = 0;
        totalPage = reader.NumberOfPages;
        pageSize = totalPage / unitSize;
        remainder = totalPage % unitSize;

        // 足够20的分割文件
        int currentIndex = 0;
        for (int index = 0; index < pageSize; index++)
        {
            currentIndex = (index + 1);
            using (Document document = new Document())
            {
                int sv = (startPage + index * unitSize);
                int ev = ((index + 1) * unitSize);
                string newFilePath = Path.Combine(outputFolder, $"page_{sv}_{ev}.pdf");
                PdfCopy copy = new PdfCopy(document, new FileStream(newFilePath, FileMode.Create));
                document.Open();

                for (int i = sv; i <= ev; i++)
                {
                    copy.AddPage(copy.GetImportedPage(reader, i));
                }

                document.Close();
                copy.Close();
            }
        }

        // 不足20页的文件
        using (Document document = new Document())
        {
            int sv = (startPage + pageSize * unitSize);
            int ev = (pageSize * unitSize + remainder);
            string newFilePath = Path.Combine(outputFolder, $"page_size_{sv}_{ev}.pdf");
            PdfCopy copy = new PdfCopy(document, new FileStream(newFilePath, FileMode.Create));
            document.Open();

            for (int i = sv; i <= ev; i++)
            {
                copy.AddPage(copy.GetImportedPage(reader, i));
            }

            document.Close();
            copy.Close();
        }
    }
}