I am installing 5/8" thick engineered wood. (Kentwood Originals 15mm)

I have carpet in some areas currently. The house is fairly new (built in 2007).
The builder used 1/2" thick particle board on top of 3/4" OSB. Supposedly, this is done to raise the carpet height. The problem is I have some built in shelves and desk with file drawers in the room. They are both sitting on top of the particle board.

I want to remove the particle board to match the height of the existing engineered wood floor outside the room. Also, the staple penetration into the OSB will be reduced due to the thickness of the particle board. Any water spill would be destructive for the particle board as well.

Would you suggest just leaving the particle board under the desk and book shelf? Just cut around it some how? If so, what would be the best way to cut it? I have one of those door moulding saws I could try to use.

I would like to know what pros would do when they encounter this type of situation. I know I opened a can of worms, but I want to do this right the first time.

Thanks.

If stapling I would cut it out. Use a toe kick saw for this. You can rent them at Home Depot.