Visual Studio 2010 and Autocad Import

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C#

I just started studying C#. Yes I'm a newbie.
Through Microsoft Visual Studio 2010, I would like to import the drawing I created in Autocad.

http://exchange.autodesk.com/autocadarchitecture/enu/online-help/browse#WS73099cc142f48755f2fc9df120970276f7-5354.htm[^]
is the autodesk website where I followed the process, and here's the following code I copied.

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;

 
[assembly: CommandClass(typeof(MyFirstProject1.Class1))]
 
namespace MyFirstProject1
{
  public class Class1
  {
      [CommandMethod("AdskGreeting")]
      public void AdskGreeting()
      {
          // Get the current document and database, and start a transaction
          Document acDoc = Application.DocumentManager.MdiActiveDocument;
          Database acCurDb = acDoc.Database;
 
          // Starts a new transaction with the Transaction Manager
          using (Transaction acTrans = acCurDb.TransactionManager.StartTransaction())
          {
              // Open the Block table record for read
              BlockTable acBlkTbl;
              acBlkTbl = acTrans.GetObject(acCurDb.BlockTableId,
OpenMode.ForRead) as BlockTable;
 
              // Open the Block table record Model space for write
              BlockTableRecord acBlkTblRec;
              acBlkTblRec = acTrans.GetObject(acBlkTbl[BlockTableRecord.ModelSpace],
OpenMode.ForWrite) as BlockTableRecord;
 
              /* Creates a new MText object and assigns it a location,
              text value and text style */
              MText objText = new MText();
 
              // Specify the insertion point of the MText object
              objText.Location = new Autodesk.AutoCAD.Geometry.Point3d(2, 2, 0);
 
              // Set the text string for the MText object
              objText.Contents = "Greetings, Welcome to the AutoCAD .NET Developer's Guide";
 
              // Set the text style for the MText object
              objText.TextStyleId = acCurDb.Textstyle;
 
              // Appends the new MText object to model space
              acBlkTblRec.AppendEntity(objText);
 
              // Appends to new MText object to the active transaction
              acTrans.AddNewlyCreatedDBObject(objText, true);
 
              // Saves the changes to the database and closes the transaction
              acTrans.Commit();
          }
      }
  }
}

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I'm getting errors on CommandClass, CommandMethod, Document, and Document Manager.
I referecned acdbmgd.dll, acmgd.dll(Autocad .NET API ) files, and added
using Autodesk.AutoCAD.Runtime;

However, the error says that The type or namespace could not be found.I don't get it!!