PDF转换成二进制字符串写入 HTTP 输出流

/// <summary>
/// 从文件读取 Stream
/// </summary>
public Stream FileToStream(string fileName)
{
// 打开文件
FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);
// 读取文件的 byte[]
byte[] bytes = new byte[fileStream.Length];
fileStream.Read(bytes, 0, bytes.Length);
fileStream.Close();
// 把 byte[] 转换成 Stream
Stream stream = new MemoryStream(bytes);
return stream;
}