//Server сторона:
function TServerMethods1.DownloadFile(out Size: Int64): TStream;
begin
    Result := TFileStream.Create('upload.fil', fmOpenRead or fmShareDenyNone);
    Size := Result.Size;

    Result.Position := 0;
end;

//Client сторона:
procedure TfMain.DownloadFile(Sender: TObject);
var
    RetStream: TStream;
    Buffer: PByte;
    Mem: TMemoryStream;
    BytesRead: Integer;
    DocumentId: Int64;
    Size: Int64;
    filename: WideString;
    BufSize: Integer;
begin
    BufSize := 1024;

    try
      Mem := TMemoryStream.Create;
      GetMem( Buffer, BufSize );

      try
        RetStream := FDownloadDS.DownloadFile(Size);
        RetStream.Position := 0;

        if ( Size <> 0 ) then
        begin
          filename := 'download.fil';

          repeat
            BytesRead := RetStream.Read( Pointer( Buffer )^, BufSize );

            if ( BytesRead > 0 ) then
            begin
              Mem.WriteBuffer( Pointer( Buffer )^, BytesRead );
            end;

            lStatus.Caption := IntToStr( Mem.Size ) + '/' + IntToStr( Size );
            Application.ProcessMessages;

          until ( BytesRead < BufSize );

          if ( Size <> Mem.Size ) then
          begin
            raise Exception.Create( 'Error downloading file...' );
          end;
 
        Mem.SaveToFile('c:\Test.pdf');
        end
        else
        begin
          lStatus.Caption := '';
        end;
      finally
        FreeMem( Buffer, BufSize );
        FreeAndNIl(Mem);
      end;
    except
      on E: Exception do
      begin
        lErrorMessage.Caption := PChar( E.ClassName + ': ' + E.Message );
      end;
    end;
end;

...
finally
   FreeMem( Buffer, BufSize );
   FreeAndNIl(Mem);
   FreeAndNil(RetStream);
end;

function TServerMethods1.DownloadFile(out Size: Int64): TStream;
begin
    Result := TFileStream.Create('upload.fil', fmOpenRead or fmShareDenyNone);
    Size := Result.Size;
    Result.Position := 0;
end;

function TServerMethods2.GetFileFromServer(out Size: int64; f_name, Puth_file_tek, user_n, user_c: string): TStream;
var
  fStream1: TFileStream;
begin
  fStream1 := TFileStream.Create(Puth_file_tek + '\' + f_name, fmOpenRead or fmShareDenyNone);
  try
    Size := fStream1.Size;
    fStream1.Position := 0;
    Result := fStream1;
  finally
    FreeAndNil(fStream1);

  end;
end;

repeat
BytesRead := RetStream.Read( Pointer( Buffer )^, BufSize );
RetStream.Free; !!!!!!!!!!!

function TServerMethods2.GetFileFromServer2(out Size: int64): TStream;
var
  gFilemm: TStream;
begin
  gFilemm := TFileStream.Create('c:\Test.xlsx', fmOpenRead or fmShareDenyNone);
  try
    Result := TMemoryStream.Create;
    Result.CopyFrom(gFilemm, 0);
    Size := Result.Size;
    Result.Position := 0;
  finally
    FreeAndNil(gFilemm);
  end;
end;