It seems that the Application.HelpCommand is not yet implemented. I found this info in the Lazarus forum at this URL:
http://www.lazarus.freepascal.org/index.php?topic=1834.0But it's quite old (feb 2006). Is there any change since ? I can charge the help file name by Application.Helpfile, but Application.HelpCommand always returns false and does nothing.
Just for information: nothing new since, and no plans in that direction ?