Unable to add dwmapi.dll in Visual Studio

Its simple, you cannot add a reference to the DWM of the windows, BUT you can import it by using the DllImport (http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.dllimportattribute.aspx[^])

What I usually do is:

Create the following class:

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Interop;
using System.Windows.Media;

namespace WpfApplication1
{
    public static class GlassLib
    {
        struct MARGINS
        {
            public MARGINS(Thickness t)
            {
                Left = (int)t.Left;
                Right = (int)t.Right;
                Top = (int)t.Top;
                Bottom = (int)t.Bottom;
            }
            public int Left;
            public int Right;
            public int Top;
            public int Bottom;
        }

        [DllImport("dwmapi.dll", PreserveSig = false)]
        static extern void DwmExtendFrameIntoClientArea(
            IntPtr hwnd, ref MARGINS margins);

        [DllImport("dwmapi.dll", PreserveSig = false)]
        static extern bool DwmIsCompositionEnabled();

        // Extension Method for the window
        public static void ApplyGlass(this Window window)
        {
            try
            {
                if (DwmIsCompositionEnabled())
                {
                    IntPtr hwnd =
                        new WindowInteropHelper(window).Handle;
                    if (hwnd == IntPtr.Zero)
                        throw new InvalidOperationException(
                            "The Window must be shown before extending glass.");

                    window.Background = Brushes.Transparent;
                    HwndSource.FromHwnd(hwnd).CompositionTarget.BackgroundColor =
                        Colors.Transparent;

                    // Setting the MARGINS to -1 in all directions will
                    // cover the client area with Glass Effect
                    MARGINS margins = new MARGINS(new Thickness(-1));
                    DwmExtendFrameIntoClientArea(hwnd, ref margins);
                }
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }
    }
}

Then in the Window you want to add the Glass Effect you do:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        Loaded += new RoutedEventHandler(MainWindow_Loaded);
    }

    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        this.ApplyGlass();
    }
}

Build, Run, and there you go GLASS..

Note that in order for this to work you must either have a Windows OS 6 (Vista) or greater OR handle the Exception that WILL be thrown by the ApplyGlass Method.

Hope this helps

All Best,

Raul Mainardi Neto