Reads a part of the document to load.
This will be used to initially load the document when a client initiates displaying a document.
Please note, that the read method will be called only once during a server-side document read
lifecycle. Subsequent reads will trigger the recover method, not a read.
Partially recovers a Document identified by the given
PageSegmentHandle. Sometimes, client applications may request
Document instances that have either been removed from cache,
garbage-collected due to long inactivity or in consequence of a server switch.
This method will be used for subsequent document reads.