You're absolutely right that you don't want to use absolute path. Under no circumstances you should. For help files, the best way to locate them relative to the directory of the main module of the entry assembly of your application (which you probably indent to do).
You can find you binary path like this:
string binaryPath =
(By the way,
(referred to in other answer) is 100% irrelevant to this. This string shows a list of directories where you put private assemblies. Probably, you don't have any, then
. It would be pretty difficult to find anything relative to