I just failed to really crop permanently the file with Acrobat7.
I saved the pseudo cropped PDF file as a ps, used Distiller to create a new PDF out of it with a special page model. No way, I still have lot of whitespace around it.
This does not mean though that it's impossible because I read several pages about it. "Refrying" is said to work for this.
Well, "langue au chat!"
