Many thanks ! I found out what I needed to know.

It works a treat ! Thanks again for the advice. In Illustrator, after adding plenty more nodes (Object menu) one goes back th the same menu for "Simplify" then choose "straight lines" (in fact I use a French set up, I assume those are the English terms used in the menus). Once in Sketchup, the Makefaces plug-in is essential to enable push-pull extrusion. All this enables one to convert vectorized texte or logos into 3D forms. Cool.