A document is something tangible that records communication or facts, with the help of marks, words, or symbols.
A document serves to establish one or several facts and can be relied upon as proof. Therefore, it is anything which may be preserved, or represented, in order to serve as evidence for some purpose.
An office document is a piece of paper or a set of papers containing official information. These documents enable accurate information to be kept, on goods that have been sold or purchased.
In book-keeping they are referred to as source documents.