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assignfile(text, 'text.txt');
  {$I-}
   reset(text);
  {$I+}
   if IOResult > 0 then
    begin
     rewrite(text);
    end;

// -> For Schleife ???

   readln(text, prfdat);

   if prfdat = 'Wert' then
    begin
     close;
    end
   else
    begin
    .
    .
    end;
   end.					

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procedure TForm1.Button1Click(Sender: TObject);
var
  I: Integer;
  Found: Boolean;
begin

  Found := False;

  with TStringList.Create do
    try
      LoadFromFile('text.txt');
      for I := 0 to Count - 1 do
        if Strings[I] = PrfDat then
        begin
          Found := True;
          Break;
        end;
    finally
      Free;
    end;

  if Found then
    Self.Close;

end;					

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While not Eof(Text) do
Begin
    ReadLn(...);
    //Do whatever you want
end;