Vaya a Formato ▸ Organizar ▸ Enviar al fondo (LibreOffice Writer, %[officename] Calc).
Vaya a Forma ▸ Organizar ▸ Enviar al fondo (LibreOffice Draw).
⇧⌘-Mayús + Ctrl + signo de resta (LibreOffice Impress, LibreOffice Draw)
Open context menu - choose Arrange - Send to Back (LibreOffice Impress).