Windows 10 user see this post: How to open EPANET’s help file on Windows 10?
I get this question from time to time from people who are unable to open the EPANet help file in Windows 7. Actually, the help file may not open also on Windows Vista, Windows Server 2008, or Windows Server 2008 R2. The error message some people see is some variation of the following:
The Help for this program was created in Windows Help format, which depends on a feature that isn’t included in this version of Windows. However, you can download a program that will allow you to view Help created in the Windows Help format.
I can’t understand why the good people over at Microsoft decided not to include the conversion program in Windows 7 at the first place but you may download it from Microsoft support web site.
Scroll down to the ‘Resolution’ section and select the Windows Help program suitable for your operating system.