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;