The DLL file is not required to use RoboHelp for Word but it is required to be installed on end user PCs if you are distributing WinHelp output. Your RoboHelp licence allows for you to freely distribute it to any end user PC that needs it. Are you distributing WinHelp? If so, have you looked at other outputs available in the RoboHelp HTML Help application that are more up to date and do not suffer from file distribution issues.
@Colum - I think your statement should be amended to read instead:
The DLL file is not required to use RoboHelp for Word but it *MAY BE* is required to be installed on end user PCs if you are distributing WinHelp output.
I suggest this because I don't believe it's a requirement to distribute unless you are using certain RoboHelp specific features with the WinHelp output.
Oops, forgot to add that even other outputs using RoboHelp HTML *MAY* also require additional distribution.
I'm thinking HHActiveX.dll here for CHM files using Browse Sequences or the Glossary tab.