The IDocumentInfo type exposes the following members.
Returns a document format
Indicates whether specific file is encrypted and requires password for opening. For the document types, that cannot be encrypted (like all text-based) should always return 'false'.
In implementing type should return count (number) of pages or other similar format-dependent entities (tabs, slides etc.). For those family types, that don't have something similar (like plain text documents or XML) should return 1.
Document size in bytes