using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System;
using System.IO;
using System.Windows.Media.Media3D;


namespace WpfApplication1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{

    public MainWindow()
    {
        InitializeComponent();
    }

    Model3DGroup group = HelixToolkit.Wpf.ModelImporter.Load(@"C:Jack_ShephardJack_Shephard.obj");
     public static Model3DGroup Load(string path)
    {
        if (path == null)
        {
            return null;
        }

        Model3DGroup model = null;
        string ext = System.IO.Path.GetExtension(path).ToLower();
        switch (ext)
        {
            case ".3ds":
                {
                    var r = new HelixToolkit.Wpf.StudioReader();
                    model = r.Read(path);
                    break;
                }

            case ".lwo":
                {
                    var r = new HelixToolkit.Wpf.LwoReader();
                    model = r.Read(path);

                    break;
                }

            case ".obj":
                {
                    var r = new HelixToolkit.Wpf.ObjReader();
                    model = r.Read(path);
                    break;
                }

            case ".objz":
                {
                    var r = new HelixToolkit.Wpf.ObjReader();
                    model = r.ReadZ(path);
                    break;
                }

            case ".stl":
                {
                    var r = new HelixToolkit.Wpf.StLReader();
                    model = r.Read(path);
                    break;
                }

            case ".off":
                {
                    var r = new HelixToolkit.Wpf.OffReader();
                    model = r.Read(path);
                    break;
                }

            default:
                throw new InvalidOperationException("File format not supported.");
        }

        return model;
    }

}
}

Model3DGroup group = HelixToolkit.Wpf.ModelImporter.Load(@"Your path here");

<HelixToolkit:FileModelVisual3D x:Name="model1" Source="C:$pathtest_obj.obj"/>