A Document Management System (DMS) is a computer system (or a set of computer programs) used to track and store electronic documents. It is usually also capable of keeping track of the different versions modified by different users (history tracking). The term has some overlap with the concepts of content management systems. It is often viewed as a component of enterprise content management (ECM) systems and related to digital asset management, document imaging, workflow systems and records management systems (Wikipedia)
Liferay provides out of the box a Document Management System known as Documents and Media
Each scope in Liferay gets its own separate repository where any kind of document can be stored (images, videos, documents, files...) and the security of those documents will be handled by Liferay permissions system.
Documents can be propertly organized in folders and subfolders. Every time a document is updated, a new version is created, allowing users not to lose any data at all. Users can add additional metadata to the documents using document types.
The documents stored in Documents and Media can be persisted in many different systems, such as CMISStore, DBStore, S3Store and it can be extended to support any other custom store.
Documents and Media can also be integrated with many other external repositories. Since version 6.0, Liferay supports CMIS 1.0 and it can consume any external repository that exposes CMIS protocol, such as Alfresco, Nuxeo, Documentum, Sharepoint, etc.
Also, beginning with version 7.0, the Document Management UI will be extensible with the new Display Context mechanism.