Someone with more legal knowledge might correct me, but I do not think one can be pardoned, or offer a pardon, preemptively, i.e., even before one is indicted or sentenced.
A previous reply many pages back on this same topic indicated that, effectively, you can be pardoned pre-emptively, that is, before indictment. I can't remember the legal wording needed to accomplish that, but I seem to remember that it has the effect of stopping an investigation.
But as others have written, it didn't sound as if you could be pardoned for a crime you may commit in the future. I guess THAT is beyond the pale.

I can see the purpose of a pardon for someone in jail, for humanitarian reasons maybe, or to have a trivial crime expunged so you can live a normal life, but being pardoned for something for which the investigation is not yet completed, so you don't even know how serious it is yet, seems odd to me. Doesn't sound like the kind of absolute power you want anyone in a democracy to have.