Can I install the new version of windows microsoft office without my authorisation key?

I have windows vista but I can't access my microsoft office word as you need an authorisation key for my laptop plus it is has run out of it's trial free usage. The computer was given to me by my mum and she does not remember the authorisation key code. I want to buy a new version of microsoft office word and install it. The question is would I need the authorisation key to install the new version? If i do how do I get around it so that I can install it?