Imports Autodesk.AutoCAD.Runtime
Imports Autodesk.AutoCAD.ApplicationServices
Public Class class1
    <CommandMethod("CreateImage")> _
    Public Shared Sub CreateImage()
        'zoom extents... need to use .NET 4.0 
        Dim acad = Application.AcadApplication
        acad.ZoomExtents()
        Dim doc As Document = Application.DocumentManager.MdiActiveDocument
        Using image As Drawing.Bitmap = doc.CapturePreviewImage(3760, 2920)
            'save the image...
            image.Save("c:\test.png", System.Drawing.Imaging.ImageFormat.Png)
        End Using
    End Sub
End Class