Symptoms
Word Documents Event Object reference not set to an instance of an object error
Diagnoses
Using Word Documents Event to Update Document Content Control is getting error. The Event configuration is everything looks correct.
"5513996","2015-08-19 15:17:23","Error","General","28083","ExtenderExecuteError","ProcessInstance.HandleException","28083 ServerEvent: Server was unable to process request. ---> Object reference not set to an instance of an object.
InnerException: Exception has been thrown by the target of an invocation.
Resolution
There is no Word Documents event for SP 2013 ... But there are a few alternatives you can try
https://startrule.wordpress.com/2015/05/22/word-documents-event-wizard-for-sharepoint-2013/
http://community.k2.com/t5/K2-blackpearl/Updating-Word-Document-content-using-K2-and-SharePoint-2013/td-p/79330