网上有很多获取pdf页数方法有读流判断type/page的但是经过实际测试文件太大的时候往往不是很准确，既然这样我们就不用费心去自己写了可以用itextsharp。

这里是下载地址：http://sourceforge.net/projects/itextsharp/files/

（1）创建一个Windows控制台应用程序，命名为ReadPdfDemo。
（2）添加对iTextSharp的引用。
（3）在“Program.cs”文件中添加如下引用。
using System;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
（4）直接修改“Program.cs”文件的代码如下。
namespace ReadPdfDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("读取PDF文档");
            try
            {
                // 创建一个PdfReader对象
                PdfReader reader = new PdfReader(@"C:\origin.pdf");
                // 获得文档页数
                int n = reader.NumberOfPages;
                // 获得第一页的大小
                Rectangle psize = reader.GetPageSize(1);
                float width = psize.Width;
                float height = psize.Height;
                // 创建一个文档变量
                Document document = new Document(psize, 50, 50, 50, 50);
                // 创建该文档
                PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(@"C:\Read.pdf", FileMode.Create));
                // 打开文档
                document.Open();
                // 添加内容
                PdfContentByte cb = writer.DirectContent;
                int i = 0;
                int p = 0;
                Console.WriteLine("一共有 " + n + " 页.");
                while (i < n)
                {
                    document.NewPage();
                    p++;
                    i++;
                    PdfImportedPage page1 = writer.GetImportedPage(reader, i);
                    cb.AddTemplate(page1, .5f, 0, 0, .5f, 0, height / 2);
                    Console.WriteLine("处理第 " + i + " 页");
                    if (i < n)
                    {
                        i++;
                        PdfImportedPage page2 = writer.GetImportedPage(reader, i);
                        cb.AddTemplate(page2, .5f, 0, 0, .5f, width / 2, height / 2);
                        Console.WriteLine("处理第 " + i + " 页");
                    }
                    if (i < n)
                    {
                        i++;
                        PdfImportedPage page3 = writer.GetImportedPage(reader, i);
                        cb.AddTemplate(page3, .5f, 0, 0, .5f, 0, 0);
                        Console.WriteLine("处理第 " + i + " 页");
                    }
                    if (i < n)
                    {
                        i++;
                        PdfImportedPage page4 = writer.GetImportedPage(reader, i);
                        cb.AddTemplate(page4, .5f, 0, 0, .5f, width / 2, 0);
                        Console.WriteLine("处理第 " + i + " 页");
                    }
                    cb.SetRGBColorStroke(255, 0, 0);
                    cb.MoveTo(0, height / 2);
                    cb.LineTo(width, height / 2);
                    cb.Stroke();
                    cb.MoveTo(width / 2, height);
                    cb.LineTo(width / 2, 0);
                    cb.Stroke();
                    BaseFont bf = BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
                    cb.BeginText();
                    cb.SetFontAndSize(bf, 14);
                    cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, "page " + p + " of " + ((n / 4) + (n % 4 > 0 ? 1 : 0)), width / 2, 40, 0);
                    cb.EndText();
                }
                // 关闭文档
                document.Close();
            }
            catch (Exception de)
            {
                Console.Error.WriteLine(de.Message);
                Console.Error.WriteLine(de.StackTrace);
            }
        }
    }
}

使用iTextSharp读取PDF文档