function O_o(FileName: String): String;
var
   f: File;
   P, Pt: Pointer;
   Size, i: DWord;
 
   function DecToBin(Dec, Digits, CompareDigit: DWord): String;
   var
      i: Integer;
   begin
      Result := '';
      // CompareDig := Round(Exp(Digits * Ln(2)) / 2);
      for i := 0 to Digits - 1 do
         Result := Result + IntToStr(Integer(Dec and (CompareDigit shr i) > 0));
   end;
 
begin
   Result := '';
   AssignFile(f, FileName);
   Reset(f, 1);
   Size := FileSize(f);
   GetMem(Pt, Size);
   P := Pt;
   BlockRead(f, P^, Size);
   CloseFile(f);
   for i := 1 to Size do begin
      Result := Result + DecToBin(Byte(P^), 8, 128);
      P := Pointer(DWord(P) + 1);
   end;
   FreeMem(Pt, Size);
end;

Form1.Memo1.Text := O_o('Test.txt');