What is the difference between files and documents

In DOCman, there are two concepts: files and documents. 

A file is is a physical file, that was uploaded to DOCman and is stored on the filesystem of the server.

A document is more than that: a document is the combination of a file, along with all it's metadata such as title, description, permissions, license, thumbnail, dates, published state, ... So when a user browses the DOCman front-end, he or she sees a list of documents (including metadata). When the users clicks the download button, the file is downloaded to the user's computer.