A bare-bones example of how to write alternate data streams with C#

CSharpBasicAlternateDataStream

using Microsoft.Win32.SafeHandles;
using System;
using System.IO;
using System.Runtime.InteropServices;

namespace AlternateDataStreams
{
    class Program
    {
        [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        public static extern SafeFileHandle CreateFile(
           string lpFileName,
           EFileAccess dwDesiredAccess,
           EFileShare dwShareMode,
           IntPtr lpSecurityAttributes,
           ECreationDisposition dwCreationDisposition,
           EFileAttributes dwFlagsAndAttributes,
           IntPtr hTemplateFile);

        static void Main(string[] args)
        {
            string basePath = @"c:\Users\tekhe\temp\";
            string baseFile = "funwithfiles.txt";

            //First create a vanilla text file
            File.WriteAllText(Path.Combine(basePath, baseFile), "This is the normal, unnamed data stream.");

            //Write an image to the ADS
            CreateFileWithAlternateDataStream(basePath, baseFile, ":TheKitten", "kitten.jpg");

            //Write a PDF to the ADS
            CreateFileWithAlternateDataStream(basePath, baseFile, ":PDFSample", "pentest.pdf");

            Console.WriteLine("Done");
            Console.ReadKey();

        }

        static void CreateFileWithAlternateDataStream(string basePath, string baseFile, string streamName, string fileToWrite)
        {
            var sfh = CreateFile(basePath + baseFile + streamName,
                   EFileAccess.GenericRead | EFileAccess.GenericWrite,
                    EFileShare.Read,
                    IntPtr.Zero,
                    ECreationDisposition.CreateAlways,
                    EFileAttributes.Normal,
                    IntPtr.Zero);

            if (sfh.IsInvalid)
            {
                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
            }

            using (FileStream fs = new FileStream(sfh, FileAccess.Write))
            {
                byte[] filebytes = File.ReadAllBytes(Path.Combine(basePath, fileToWrite));
                fs.Write(filebytes, 0, filebytes.Length);
            }

            sfh.Close();
        }
    }
}

[Flags]
enum EFileAccess : uint
{
    GenericRead = 0x80000000,
    GenericWrite = 0x40000000,
    GenericExecute = 0x20000000,
    GenericAll = 0x10000000
}

[Flags]
public enum EFileShare : uint
{
    None = 0x00000000,
    Read = 0x00000001,
    Write = 0x00000002,
    Delete = 0x00000004
}

public enum ECreationDisposition : uint
{
    New = 1,
    CreateAlways = 2,
    OpenExisting = 3,
    OpenAlways = 4,
    TruncateExisting = 5
}

[Flags]
public enum EFileAttributes : uint
{
    Normal = 0x00000080
}