Buffer: WideString;
...
FileStm = TFileStream.Create(...)
 Buffer = SysAllocStringByteLen(размер файла)
 FileStm.ReadBuffer(Buffer, размер файла)
   SignedData.Content:=Buffer;

function _to_utf8_hex(s) {
    var c, d = "";
    for (var i = 0; i < s.length; i++) {
        c = s.charCodeAt(i);
        if (c <= 0x7f) {
            d += _to_hex(c)
        } else if (c >= 0x80 && c <= 0x7ff) {
            d += _to_hex(((c >> 6) & 0x1f) | 0xc0);
            d += _to_hex((c & 0x3f) | 0x80)
        } else {
            d += _to_hex((c >> 12) | 0xe0);
            d += _to_hex(((c >> 6) & 0x3f) | 0x80);
            d += _to_hex((c & 0x3f) | 0x80)
        }
    };
    return d
}

function SignTextWorker(SigData, Signer, silent, data) {
    if (data.convert_to_utf8 == 1) {
        var CU = getCAPICOMObject("Utilities"),
            text = _to_utf8_hex(data.text);
        if (text.length % 4) text += '00';
        SigData.Content = CU.HexToBinary(text)
    } else SigData.Content = data.text;
    return SigData.Sign(Signer, false, CAPICOM_ENCODE_BASE64)
}

function ToCAPICOM(input: string) : string;
var
  ch: Char;
  i, code: Integer;

begin
  Result := '';
  for i := 1 to input.Length do
  begin
    code := Ord(input[i]);

    if code <= 127 then
    begin
      Result := Result + IntToHex(code, 2);
    end
    else if (code >= 128) and (code <= 2047) then
    begin
      Result := Result + IntToHex((((code shr 6) and 31) or 192), 2);
      Result := Result + IntToHex(((code and 63) or 128), 2);
    end
    else
    begin
      Result := Result + IntToHex(((code shr 12) or 224), 2);
      Result := Result + IntToHex((((code shr 6) and 63) or 128), 2);
      Result := Result + IntToHex(((code and 63) or 128), 2);
    end;

  end;

  if Result.Length mod 4 > 0 then
  begin
    Result := Result + '00';
  end;
end;


 //Подпись
function podpis(input: String) : String;
begin

    Utils:=CreateOleObject('CAPICOM.Utilities');
    Signer.Certificate := Crt;
    SignedData.Content:= Utils.HexToBinary(ToCAPICOM(input));
    podpis := SignedData.Sign(Signer, false, 0);

end;