Whenever I have to pull up tack strips I use a mini pry bar such as in the picture. They can be purchased on Amazon and many other sites, and also in home improvement centers.
I think you are referring to smooth edge that was used to install carpet on an existing hardwood floor. If that's the scenario,use a pair of pinchers that you can pinch them into the smooth edge where the nails are. It will split the plywood at every nail but its the only way you dont have to pry down on the hardwood. Its the least damaging way to remove the nails. If the smooth edge is too close to the baseboard to get the pinchers in, then use a cats paw. Its a small bar about 10 inches long with a nail puller on the end of it. Use a hammer to drive it down under the nail heads the pry the nails out. The trick is to hold the bar at the right angle before you pound on it with your hammer.
Here's a post about it. https://www.ehow.com/how_5651998_remove-tack-strips-hardwood-floors.html Hope it helps!