File.Split Method

public static void Split(string fileInputPath,
     string folderOutputPath,
     int countOfOutputFiles)
 {
     byte[] byteSource = System.IO.File.ReadAllBytes(fileInputPath);
     FileInfo fiSource = new FileInfo(fileInputPath);
     int partSize = (int)Math.Ceiling((double)(fiSource.Length / countOfOutputFiles));
     int fileOffset = 0;
     string currPartPath;
     FileStream fsPart;
     int sizeRemaining = (int)fiSource.Length;
     for (int i = 0; i < countOfOutputFiles; i++)
     {
         currPartPath = folderOutputPath + "\\" + fiSource.Name + "." + string.Format(@"{0:D4}", i) + ".part";
         if (!System.IO.File.Exists(currPartPath))
         {
             fsPart = new FileStream(currPartPath, FileMode.CreateNew);
             sizeRemaining = (int)fiSource.Length - (i * partSize);
             if (sizeRemaining < partSize)
                 partSize = sizeRemaining;
             fsPart.Write(byteSource,
                 fileOffset,
                 partSize);
             fsPart.Close();
             fileOffset += partSize;
         }
     }
 }