Windows Forms - Enter keypress activates submit button?

If you set your Form's AcceptButton property to one of the Buttons on the Form, you'll get that behaviour by default.

Otherwise, set the KeyPreview property to true on the Form and handle its KeyDown event. You can check for the Enter key and take the necessary action.

You can designate a button as the "AcceptButton" in the Form's properties and that will catch any "Enter" keypresses on the form and route them to that control.

See How to: Designate a Windows Forms Button as the Accept Button Using the Designer and note the few exceptions it outlines (multi-line text-boxes, etc.)

As previously stated, set your form's AcceptButton property to one of its buttons AND set the DialogResult property for that button to DialogResult.OK, in order for the caller to know if the dialog was accepted or dismissed.

The Form has a KeyPreview property that you can use to intercept the keypress.

Set the KeyPreview attribute on your form to True, then use the KeyPress event at your form level to detect the Enter key. On detection call whatever code you would have for the "submit" button.