As it was boring to get a 3D printable solution for my objects witch are "2D",
Jacinto Costoso found for me a Blender way ! Solidify :
From a wrl I can make a x3d with Fluxstudio,
then I enter it in Blender, I solidify ! I export as *.obj
Of course if I start from an obj that enters in Blender.
About holes :
Select all holes in a mesh and fill them
Shift+M* selects all Non-manifold edges/vertices (holes) in a mesh **. Then all you have to do is hit Ctrl+F to auto-fill those holes with "beauty fill".
Shift+M is an alternative shortcut for 'Select Non-manifold'. You'll find this in the select menu when in mesh edit mode. The listed short cut there is Ctrl+Alt+Shift+M. Shift M is obviously a lot more comfortable on the fingers though!
Although 'Non-manifold' usually refers to holes in your mesh, it is not necessarily only holes e.g., an edge with three faces coming out of it is also a non-manifold edge!