Solution :

First of all you have to know that before any copy or replace database files, you have to set the database in offline state and get it back online after finish.

1) Used Methods

 // fullPath : the path for your database
 // executablePath : the path for your exe folder

    void setFullPath()
    {
        string executable = System.Reflection.Assembly.GetExecutingAssembly().Location;
        executablePath = (System.IO.Path.GetDirectoryName(executable));
        fullPath = executablePath + "\\Database.mdf";
    }

    void takeOffline(string fullPath)
    {
        homeObject.connection.Open();
        homeObject.cmd.CommandText = "ALTER DATABASE [" + fullPath + "] SET OFFLINE";
        homeObject.cmd.ExecuteNonQuery();
        homeObject.cmd.Clone();
    }

    void bringOnline(string fullPath)
    {
        homeObject.cmd.CommandText = "ALTER DATABASE [" + fullPath + "] SET ONLINE"; ;
        homeObject.cmd.ExecuteNonQuery();
        homeObject.cmd.Clone();
        homeObject.connection.Close();
    }

2) Copy database files / Backup

  bool getDatabaseCopy()
    {
        try
        {
            //
            takeOffline(fullPath);

            // copy database.mdf
            copyDBMDF();

            // copy database_log.ldf
            copyDB_logLDF();

            //
            bringOnline(fullPath);

            return true;
        }
        catch
        {
            //
        }

        return false;
    }

    // txtPath.txt :
    // folder location to save database files in

    void copyDBMDF()
    {
        string fileName = "Database.mdf";

        string sourceFile = fullPath;
        string targetPath = txtPath.Text;

        // Use Path class to manipulate file and directory paths.
        string destFile = System.IO.Path.Combine(targetPath, fileName);

        // To copy a folder's contents to a new location:
        // Create a new target folder, if necessary.
        if (!System.IO.Directory.Exists(targetPath))
        {
            System.IO.Directory.CreateDirectory(targetPath);
        }

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

    void copyDB_logLDF()
    {
        string fileName = "Database_log.ldf";

        string sourcePath = executablePath;
        string targetPath = txtPath.Text;

        // Use Path class to manipulate file and directory paths.
        string sourceFile = System.IO.Path.Combine(sourcePath, fileName);
        string destFile = System.IO.Path.Combine(targetPath, fileName);

        // To copy a folder's contents to a new location:
        // Create a new target folder, if necessary.
        if (!System.IO.Directory.Exists(targetPath))
        {
            System.IO.Directory.CreateDirectory(targetPath);
        }

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

3) Replace current database files with files you copy / Restore

  bool restoreTheBackup()
    {
        try
        {
            //
            takeOffline(fullPath);

            // load .mdf
            loadMDFDatabaseFile();

            // load _log.ldf
            loadLDFDatabaseFile();

            //
            bringOnline(fullPath);

            return true;
        }
        catch
        {
            //
        }

        return false;
    }

// txtPath.txt :
// location to get database files from to replace with current files.

    void loadLDFDatabaseFile()
    {
        string fileName = "Database_log.ldf";

        string targetPath = executablePath;
        string sourcePath = txtPath.Text;

        // Use Path class to manipulate file and directory paths.
        string sourceFile = System.IO.Path.Combine(sourcePath, fileName);
        string destFile = System.IO.Path.Combine(targetPath, fileName);

        // To copy a folder's contents to a new location:
        // Create a new target folder, if necessary.
        if (!System.IO.Directory.Exists(targetPath))
        {
            System.IO.Directory.CreateDirectory(targetPath);
        }

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

    void loadMDFDatabaseFile()
    {
        string fileName = "Database.mdf";

        string targetPath = executablePath;
        string sourcePath = txtPath.Text;

        // Use Path class to manipulate file and directory paths.
        string sourceFile = System.IO.Path.Combine(sourcePath, fileName);
        string destFile = System.IO.Path.Combine(targetPath, fileName);

        // To copy a folder's contents to a new location:
        // Create a new target folder, if necessary.
        if (!System.IO.Directory.Exists(targetPath))
        {
            System.IO.Directory.CreateDirectory(targetPath);
        }

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