Vectorisation of the outline

Hello,

On my old X7 version of Coreldraw I did this without any problem...
I draw a shape, a square for example. I magnify the outline by going from the thinnest line to a 36Pts line.Then I would like to vectorise the outline to keep this 36pt thickness but this option is not selectable. I see the option in my Bitmap tab but I can't use it. Can you help me? Thanks