Can I invert an image or do I have to do it before I import it?
you would need to place a frame around it, like a rectangle for example… then set this rectangle to any depth greater than 0 and send it to the back.
then select all, then deselect the rectangle (or just select the design if its a single piece)
Set the design to 0 depth.
Select All and Combine (Edit>Combine… OR Ctrl+J)
This will erase the original design from the framed area creating a negative of the original.