Paul
Looking into this, it is an error in the documentation (my bad! ).
The doc refers, as you say, to psWPSecret, while the actual property in the cWPWebApp.pkg is psWPEncryptSecret. This (psWPEncryptSecret) is what you should set to the entered, or generated, 32-character string from the plugin: where in the DF4WP plugin's dashboard (DataFlex for WordPress (DF4WP) Plugin Settings) it says "Secret (32 characters):".
I'll fix this in the original of that document (I just did it, in fact), but the problem with PDF's is that they are fixed. I'll talk to Data Access about correcting that.
HTH.
Mike