public Form1()
{
    InitializeComponent();
    fpSpread1.EditModePermanent = true;
    InputMap inputMap = fpSpread1.GetInputMap(InputMapMode.WhenAncestorOfFocused, OperationMode.Normal);
    object key = inputMap.Get(new Keystroke(Keys.Enter, Keys.None));
    ActionMap actionMap = fpSpread1.GetActionMap();
    actionMap.Put(key, new EnterAction());
}
public class EnterAction : FarPoint.Win.Spread.Action
{
    public override void PerformAction(object sender)
    {
        SpreadView spreadView = (SpreadView)sender;
        if (spreadView.EditMode)
        {
            if (!spreadView.StopCellEditing())
            {
                return;
            }
        }
        SheetView sheetView = spreadView.GetSheetView();
        sheetView.ActiveRowIndex++;
    }
}