1、读取文件，并转换为字节流

FileStream fs = new FileStream(filename,FileMode.Open,FileAccess.Read);

byte[] infbytes = new byte[(int)fs.Length];

fs.Read(infbytes, 0, infbytes.Length);

fs.Close();

return infbytes;

2、将字节流写入文件

FileStream fs = new FileStream("D:\inf.dlv",FileMode.Create,FileAccess.Write);

fs.Write(infbytes, 0, inf.Length);

fs.Close();

.将字节流转换成文件流

Stream stream = new MemoryStream(bytes);

return stream;