No president has done it and it certainly was not the intent of the pardon power. But it is not explicitly forbidden. Hopefully if he tries it it gets ruled against, but after SCOTUS made that horrible ruling about presidential immunity I have little confidence.
Trump getting away with a pardon and then getting assassinated is, in my mind, one of the worst scenarios. It martyrs him in the eyes of his cult. At the same time, it sets out legal precedent for a future fascist/authoritarian to pardon themselves for misdeeds in office. He's an old man anyway and won't last much longer. Let's hope it does not come to pass.
Wish granted. Those apps are now all rewritten as Swing Java applets.