uses Clipbrd, ...

//disable CTRL + V ("Paste") :: handles Edit1.OnKeyDown
procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState) ;
begin
if ((ssCtrl in Shift) AND (Key = ord('V'))) then
begin
if Clipboard.HasFormat(CF_TEXT) then ClipBoard.Clear;

Edit1.SelText := '"Paste" DISABLED!';

Key := 0;
end;
end;