public class MxdMegaMover
    {
        private String _rootFolder;
        private String _destinationFolder;
        private List<String> _mxdList;

        public String rootFolder
        {
            get { return this._rootFolder; }
        }

        public String destinationFolder
        {
            get { return this._destinationFolder; }

            set { this._destinationFolder = value; }
        }

        public List<String> mxdList
        {
            get { return _mxdList; }
        }

        public MxdMegaMover(String rootFolder,String destinationFolder)
        {
            this._rootFolder = rootFolder;
            this._destinationFolder = destinationFolder;
            this._mxdList = getMxdList();
        }

        public List<String> getMxdList()
        {
            List<String> tempList = new List<string>();
            DirectoryInfo di = new DirectoryInfo(this._rootFolder);
            FileInfo[] files = di.GetFiles("*.mxd",SearchOption.AllDirectories);
            foreach(FileInfo fi in files)
            {
                tempList.Add(fi.FullName);
            }
            return tempList;
        }

        public void moveMxd()
        {
            Type t = Type.GetTypeFromCLSID(typeof(AppRefClass).GUID);
            System.Object obj = Activator.CreateInstance(t);
            IApplication pApp = obj as IApplication;

            IMxDocument pDoc = (IMxDocument)pApp.Document;
            foreach (String documentPathname in this._mxdList)
            {
                pApp.OpenDocument(documentPathname); //this is where the error is thrown.
                pApp.SaveAsDocument(this._destinationFolder + "\\" + System.IO.Path.GetFileName(documentPathname), false);
                Console.WriteLine(documentPathname + " salvo em " + this._destinationFolder);
            }
        }

// To copy a file to another location and 
// overwrite the destination file if it already exists.
System.IO.File.Copy(sourceFile, destFile, true);

// To move a file or folder to a new location:
System.IO.File.Move(sourceFile, destinationFile);

public void ChangeMXDDataSource(String sourceMxd, String targetMxd)
{
	IMapDocument doc = new MapDocumentClass();
	doc.Open(sourceMxd, null);
	
	// change some properties... 
	
	/**IMap map = doc.get_Map(0);
	IFeatureLayer layer = (IFeatureLayer) map.get_Layer(0);
	IDataLayer2 dataLayer = (IDataLayer2) layer;
	IDatasetName name = (IDatasetName) dataLayer.DataSourceName;
	IWorkspaceName workspace = name.WorkspaceName;
	IPropertySet conn = workspace.ConnectionProperties;
	conn.SetProperty("SERVER", "new-server-name");
		
	workspace.ConnectionProperties = conn ;
	
	dataLayer.Disconnect();
	dataLayer.Connect(null);
	
	IMxdContents contents = (IMxdContents) map; 
	
	doc.ReplaceContents( contents); **/
	doc.SaveAs(targetMxd, true, true);
	  
	doc.Close();
}