private bool GetDocuContent(out byte[] Content, out string FileName, out string ExtensionName)
        {
            long MaxLength = 10485760; //10M以内
            Content = null;
            ExtensionName = string.Empty;
            FileName = string.Empty;
            OpenFileDialog vsOpenFileDialog = new OpenFileDialog();
            vsOpenFileDialog.InitialDirectory = "d:\\";
            vsOpenFileDialog.Filter = "All files (*.*)|*.*";
            vsOpenFileDialog.FilterIndex = 0;
            vsOpenFileDialog.Multiselect = false;
            try
            {
                if (vsOpenFileDialog.ShowDialog() == DialogResult.OK)
                {
                    //Path.GetExtension方法:返回指定的路径字符串的扩展名
                    ExtensionName = Path.GetExtension(vsOpenFileDialog.FileName);
                    //Path.GetFileName方法:返回指定路径字符串的文件名和扩展名。
                    FileName = Path.GetFileName(vsOpenFileDialog.FileName);
                    FileInfo vsFileInfo = new FileInfo(vsOpenFileDialog.FileName);
                    if (vsFileInfo.Length > MaxLength)
                    {
                        MessageBox.Show("文件超长！");
                        return false;
                    }
                    //vsFileInfo.OpenRead Method:Creates a read-only FileStream.
                    FileStream fileStream = vsFileInfo.OpenRead();
                    if (fileStream.Length == 0)
                    {
                        MessageBox.Show("空文件！");
                        return false;
                    }
                    Content = new byte[fileStream.Length];
                    int Size = fileStream.Read(Content, 0, Convert.ToInt32(fileStream.Length));
                    fileStream.Close();
                    return true;
                }
                return false;
            }
            catch (Exception ex)
            {
                return false;
            }
        }

小注：

1、 C# Winform OpenFileDialog 控件

2、C# FileStream.Read Method

假如选择的文件1111.png，是跟踪内容显示：

ExtensionName = Path.GetExtension(vsOpenFileDialog.FileName)

FileName = Path.GetFileName(vsOpenFileDialog.FileName)

FileInfo vsFileInfo = new FileInfo(vsOpenFileDialog.FileName)

Content = new byte[fileStream.Length]

4、假如相对返回的byte[] Content加密的话，可以使用：Convert.ToBase64String(Content)，该函数的返回值，依然是：byte[]类型的。