Paperparrot offers various attributes:
The person or institution that is either recipient or issuer of a document.
The document type describes what kind of document it's applied to. This could be something like "Paycheck", "Certificate"...
A tag can contain all kinds of information, a single tag can be assigned to many documents and a single document can have many tags. You can use tags to store all the important information that doesn't fit the correspondent or document type attributes.
The date a document was originally issued at.
The archive serial number (short: ASN) is a unique identifier for the document. This can help you to make sorting and archival of physical documents easier.