press ENTER for transfer between to textboxes

The simple answer is: "Don't"

The "normal" action of ENTER is to accept data and close, not to copy data around a form, and subverting that behaviour is a bad idea as it confuses users: they expect a behaviour with all their other applications and yours "doesn't work" - this can result in users not wanting to use your app, purely because other apps "don't do it like that".

Find another key, and just add a "transfer" button they can click if they want - then use the Form to override the ProcessCmdKey method, after setting the Form.KeyPreview property to true.