Other programs can open Help files, and if context sensitive Help has been implemented, then the other application can open the Help file on a relevant page.
Programs normally call context sensitive help by passing a 'Topic number'.
This number can be entered in the Topic dialog along side the Topic name. It is really then up to coding your program correctly. With Visual basic the topic number can be entered as one of the properties of the dialog or control. Remember to process and Build after. Also if your programmers have already provided a 'map' file you can use this instead of putting the number in yourself.