Oh, I apologize for that, I've been updating the controls over time and it seems I forgot to update the in-game controls list as well.
I'm testing and the Page Up key does work to stop your companion from following you, can you tell me on which map and at what point in the game you tried it? Maybe it's a bug.
I'm afraid the game no longer has a key to save your game at any time other than doing it from the pause menu because it was a more buggy feature.