Lenovo Yoga 730 keyboard replacement - giant black plastic?

Hello - I am replacing a keyboard on a Lenovo Yoga 730 13" and wondering what is the giant sheet of black plastic that covers the backside of the keyboard? It is sticky on the corners and sticks to the original keyboard making it difficult to remove and covers the screws so you need to remove it. Do I need to replace it too or just the keyboard? Seems impossible to remove without the plastic.

Thank you

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