When setting up a portable distribution with pre-installed plugins and handbook, then the link to the handbook is stored in the config file with absolute path. This is not portable, as the drive letter might change for an installation on mobile storage devices.

One can, however, edit the config file and just leave the relative path wrt. installation directory.
This works as long as the user does not switch the current directory after program startup.

Currently, in such situations, I have to recommend the students to run a separate pristine SMath instance and use the handbook there.

The question is, how can the path possibly refer to the installation directory (as found with SettingsDirectory() by Davide)?
Should not be too complicated as the extension manager finds the handbook anyways (after a useless error message).