Cutting GRP / composite front door to size

Hi,

I'm lifting my existing ceramic floor tiles in my hallway and replacing with stone and underfloor heating. Problem is, this will raise the floor height by about an inch or so meaning my front door won't open!

I think the door is Composite / GRP (it has a metal frame and when I lift the letterbox out it looks like fibreglass type material). Is it possible to open the metal frame at the bottom and plane an inch from the door or am I looking at a whole new front door?

Thanks - comments much appreciated...