Some further info. Both .CHM and .HSX help files can be opened in 7-Zip. The listing that is displayed is all the parts of a Help file as individual files.

Martin

It looks like Microsoft has dropped support for the ancient hlp format (WinHlp32.exe) under Windows 10 completely.

I have found a solution to install an older version of "WinHlp32.exe" under Windows 10:

1. Extract the file "WinHlp32.exe" from a Windows XP installation (Windows directory)
2. Copy the file "WinHlp32.exe" to your Windows 10 system in folder c:\temp
3. Start notepad and create a new file with the following content:

@echo off
set crtpth=%CD%
takeown /f "%windir%\winhlp32.exe" >nul
icacls "%windir%\winhlp32.exe" /grant *S-1-5-32-544:F >nul
copy /y "%crtpth%\winhlp32.exe" %windir%
icacls "%windir%\winhlp32.exe" /setowner "NT Service\TrustedInstaller" >nul
echo.
echo Done.
echo.
echo Press any key to Exit
pause >nul
exit

4. Save the file as ""c:\temp\Win10-Hlp32-Fix.cmd"
5. Open a command prompt window as Administrator (very important)
6. Switch to the directory "c:\temp"
7. Start the batch file "Win10-Hlp32-Fix.cmd"

If all goes well you can use old .hlp files on your Windows 10 system afterwards. On my Windows 10 system it worked perfectly.

For a German translation of this tip please go to the German forum: http://community.pmail.com/forums/thread/45441.aspx

You may have noticed that Microsoft have introduced a new help format to replace "*.chm", and several vendors have started adopting it. It is called Help 2.

https://en.wikipedia.org/wiki/Microsoft_Help_2   Files have file type of ".hsx".  There are no conversion aides to this format, but it turns out they are just zipped *.CHM, so renaming them  back to "*.chm" makes them readable.

But,.... Read the follow-up article: https://en.wikipedia.org/wiki/Microsoft_Help_Viewer, which is likely becoming the new Help facility MS Help 3.x

Martin