Microsoft removed the legacy Windows Help .hlp file viewer, winhlp32.exe, from Windows Vista, Windows 7, Windows Server 2008 and 2008 R2. Dating back to Windows 3.1, Microsoft says the Windows Help components have not been updated in years and no longer meets internal standards. If you have an older application that still uses .hlp files and must be able to view .hlp files Microsoft has released an add-on that will restore the viewer.
Simply download and install the Windows Help viewer and the classic help functionality will be restored.
Download Windows Help (WinHlp32.exe)