Ford’s pardon of Nixon relied heavily on a previous case (in the early ‘50s, I think), where judges rules that accepting a pardon is an implicit admission of guilt, so charges are not actually required if the pardon is accepted.
That was Burdick v. United States, 1915. It held that the pardonee must introduce the pardon into court proceedings and that, in so doing, the pardonee admits guilt. But, of course, having been pardoned, the pardonee skates.
In practice, Nixon didn't go to court. Nor would Hillary.