Reports Generation via PDF, CSV for audit purpose.
Reports can be accessed via the Reports link in Nagios.
The default one is the availability report.
With the filters, an individual host/service or hostgroup/servicegroup can be accessed.
These reports can be fetched in PDF format (in case of NagiosXI) or CSV format whenever required.
The report generation can also be done automatically, and the same can be sent via mail to mentioned recipients at respective date/time.