Thank you for these answers, but my problem is not with the printing, but with the visualization of the sheets.
To explain the situation: My colleagues work on Autocad, I on DrafSight for licensing issues, I mainly only do visualization of other people's plans - Yes, I'm a hideout ;-).
When I open Autocad plans with A0 sheets, only the A4 part is visible. the rest, which is on a grey background, was difficult to see the 2D CAD standard in place (which I couldn't change ...).
So my goal is to have an easier visualization of my presentation sheets by removing this space and having a uniform black background.
I don't understand in general the dimensions and sound plan on the original format real dimensions so when you import a plan in Draftsight from AutoCAD if you can view it in the AutoCAD space you should be able to view it in Draftsight
If you're in A3 under AutoCAD switch to A3 under Draftsight
you can enlarge your window but in any case go beyond the dotted lines