There are many different types of document and they all differ in one way or another. the most obvious is in size with common documents varying fro small till receipts to large A0 engineering drawings.
Not only do they differ in physically but also in other ways. Two of the most important differences are in:
Legal Requirements - What legal weight will be attached to them and will various authorities accept scanned images.
Retention Period - Different types of document must be retained for different lengths of time - By law.
In addition there are differing approaches to storing documents dependent on their status: