Noctua CPU coolers are shipped with a plastic protection cover at the bottom side of the cooler, which protects the contact surface against scratches and other damage. The plastic protection cover is clearly visible and there is no plastic film underneath.

The base of Noctua CPU coolers is made from hard-wearing nickel plated copper, so there's nothing to worry about if you buy a Noctua cooler second hand or if your cooler didn't come with a protection cover. Please proceed with the installation as explained in the manual.

You can simply remove the cover as shown below:

Base Protection Cover