The migration of Dark Souls from Games for Windows Live to Steam needs a little more time before it is completed.
Bandai Namco are have written on the Steam page that migration of save games and achievements will now be completed in December instead of November, which was the original target set in October.
Bandai Namco have said on the Steam Community forums that they are "working hard to finalize the process".
We are working hard to finalize the process to move your Dark Souls: Prepare to Die saves and achievements to Steam. We need to conduct additional testing and we are now targeting December to begin this process. We'll have more information in the coming weeks. Thank you very much for your patience!
It was announced in October that PC owners of Dark Souls would be able to move their progress and achievements from the dwindling Games for Windows Live to Steam free of charge.
Bandai Namco are among a long list of developers who are currently moving their older titles to Steam after rumors that Games for Windows Live would being shutting down in June of this year. This however didn't happen but developers are now seeing the benefits of moving to Steam instead.