Well, conversion involves a rather complicated form of taking. Finding something is not taking it.
You pick it up off the ground, you return it to the person, you've committed no criminal offence, you've committed no civil tort. You look at the information. Is that a criminal offence or a civil tort? I think not.
If you look at the information and form the intent of using that, I just don't know quite how the law would deal with the very scenario you've given here. Is that theft? At what point did it become theft or conversion? When the thought entered the person's head that they could use this information to commit fraud or impersonation? When they picked the wallet up, it wasn't theft or conversion. So an hour later, when they're sitting there at the kitchen table and saying, “Gee, I could actually use this information”, does that then convert the point at which they picked it up into a theft or a conversion?
Conversion is a little bit more than simply coming into possession of something. It's a pretty complicated concept in the civil sphere. I would be rather hesitant to suggest that it should be added to the criminal sphere.