Problème avec un arrière-plan qui ne veut pas disparaitre

@olivier_1439 The reason the grey color is sticking around is that it's probably not a real "Background" added to the whole page, but rather a Fill Color set directly inside the individual boxes (Text Fields) on your form. When you hit "Remove Background," Acrobat successfully deletes the main page background it sees, which is why it says the background is gone. However, the grey color stays because it's attached to the inside of the specific form boxes, and that setting is strong enough to still show up when printed, even if you set the main background to be invisible.

To fix it, to speed up the fix if many boxes are affected, you can select several fields at once by holding down the Shift key while clicking on them. Then, right-click any of the selected fields and choose "Properties..." to make changes that will apply to all of them instantly. Alternatively, if you are working on fields one by one, you must first find the "Prepare Form" button in Acrobat Pro. Once there, double-click on any grey box to open its settings window, and go to the "Appearance" section. Locate the "Fill Color" option, which is likely set to grey, and click on the color square to change it to "No Color" (the icon looks like a white square with a red slash). After saving these settings, you would continue to repeat this process for any remaining boxes that still print with the unwanted grey color.