A pretty old post, but I hope it's okay if I add my idea to this.
If the online help is being maintained, it could be located in a database. You only need to maintain the database. Changes still shows up in Online guide.
Somewhere when entering the guide, there could be a button saying "Generate PDF". That tool selects all information in the help table and generates a PDF in the same way a Report function would do.
Maybe a general button that generates all information and also a button for each section, for example if you would like to download a specific section?
Anyway, this way you only