Document analytics measure how recipients interact with shared documents. Unlike web analytics (pageviews, sessions), document analytics work at the page level inside a document - capturing how long each page was viewed and where attention dropped off.
For sales and fundraising, this turns 'I sent the proposal' from a black box into a behavioral signal. A prospect who lingered on the pricing page is showing buying intent; one who skipped the technical pages has different concerns to follow up on.
When a link requires a verified email, the email (and the name derived from it) attaches to each visit, so senders can see which contact viewed which pages.