I've added a helpfile as a tool, using hh.exe full/path/to/helpfile.chm and parameter {Word At Caret}
However, the helpfile doesn't start by searching that word. Does anybody know how to do this?

I found out, that there is an option for syntaxfiles, which allows one to define a helpfile. Doing this, calls the helpfile up in the way I wanted.

Add the following to the syntaxfile (sdf):

[::Header::]
HelpFile=full/path/to/helpfile.chm