If you need to download the offline Exchange Server 2013 help file you can download them directly from Microsoft download Center.
Currently Microsoft offers 3 versions to the Exchange Server 2013 offline files.
Exch2013PrvwHybridHelp.exe – Offline Help for Hybrid
Exch2013PrvwOnlineHelp.exe – Offline help for online exchange (office 365 next version)
Exch2013PrvwOnPremHelp.exe – In house install help file