writes "Wizards of the Coasts, holders of the TSR catalog, have released rulebooks and modules for most editions of Dungeons and Dragons through a partnership with DriveThruRPG.com. The web site, dndclassics.com, may be a little overloaded right now. Most module PDFs are $4.99 USD."
The article points out that these are all fresh scans of the old books. It's also worth noting that the decision to make these PDFs available reverses WotC's 2009 decision to stop all PDF sales
because of piracy fears. The only reference to this in the article is a quote from the D&D
publishing and licensing director: "We don't want them to go to torrent sites. Why not give them a legal route?"