AN-900: new event types for PDFs

@stroilova , @davestgermain , @mulby , @rocha , @brianhw  I used some guesswork on what "page" meant in different new event types. You can search on ".." to find my questions (I think). 
IMO this reference is not the right place to document bugs and implementation problems; I'm not sure how to describe the status field. Your input very welcome.