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If you want to paste to your Memo component only some constant text, then you may use onKeyDown event. In this event you may clear a clipboard's content and set into SelText property your constant string.

uses Clipbrd;
...
procedure TForm1.Memo1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if ((Key=Ord('V'))and(ssCtrl in Shift)) then
  begin
    Clipboard.Clear;
    Memo1.SelText:='Delphi is great';
    Key:=0;
  end;
end;