#region Is dll register
    public bool IsDllRegistered()
    {
      bool reg=true;
      RegistryKey rk=Registry.ClassesRoot.OpenSubKey("CLSID\\{AC53EFE4-94A7-47E6-BBFC-E9B9CF322299}");
      if(rk==null)
      {
        MessageBox.Show("未注册");
        reg=false;
      }
      else
      {
        MessageBox.Show("已注册");
      }
      return reg;
    }
    #endregion

    #region Open dwg file
    [DllImport(@"../ja-JP/com/DwgViewX.dll")]
    private static extern int DllRegisterServer();
    private void OpenDwgFile(string savePath)
    {
      if(!IsDllRegistered())
      {
        int i = DllRegisterServer();
        if (i >= 0)
        {
          /*
           * Inoke special function to open dwg file
           * */          
        }
        else
        {
          /*
           * Register failed and open dwg with CAD
           * */
          System.Diagnostics.Process.Start(savePath);
        }
      }
    }
    #endregion

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