Io non userei Indy.

Comunque (lato server):
procedure TMainFormServer.IdTCPServerExecute(AContext: TIdContext);
TFSFileIn: TFileStream;
AContext.Connection.IOHandler.ReadStream(TFSFileIn );

(Lato client):
TFLFileOut:= TFileStream.Create(TODFile.FileName, fmOpenRead);
IdTCPClient.IOHandler.Write(TFLFileOut, 0, true);