Google released the version 3.0 of "Documents List Data API," which includes PDF upload/download, and some other features, such as folder sharing, domain and group level ACLs, document revision history, and feed URIs that are more user friendly and RESTful. “Sharing folders is more efficient than sharing a large number of files one by one and the best thing is that folders are treated just like documents. You can share folders as "read-only", but you can also allow collaborators to add new files and to edit documents.” You can unhide shared folders in Google Docs interface via link.