Solid Hardwood, Engineered and Laminate Flooring - undercutting door jamb

I'm installing laminate flooring over a concrete slab. I have bedroom doorways that are going to have laminate in a hallway and transition to existing carpet in the bedrooms. I have a door jamb saw. How do I undercut a door jamb so I leave the carpeted bedroom side untouched? I only need to slide laminate under 1/2 of the jamb.
The other doorway off the same hall has a doorway that will go from laminate to existing vinyl linoleum and I have the same problem. And do I leave the door frame trim molding in place and undercut everything at once or remove the trim around the door and then undercut.

Think about where the endcap transition molding is going to sit. Actually cut the transition molding to fit across the doorway. Mark exactly where the flooring will need to stop and maintain expansion space.

Now, the key is using an electric undercut saw. Those hand saws make you work a chisel harder then needed, with the chance of damage.

Cut to where you need and use a sharp chisel, to make the downward cut and clean up any burrs, Sharp pocket knife to wittle back anything that didn't cut far enough.

Can you rent an electric door jamb saw at a tool rental store?

Yes. Most rental shops have undercut saws. At least here they do.

Thanks again, you always know how to resolve problems.