Choose Format - Arrange - Send to Back (LibreOffice Writer, LibreOffice Calc).
Choose Shape - Arrange - Send to Back (LibreOffice Draw).
Shift + CommandCtrl + ๋นผ๊ธฐ ๊ธฐํธ(-) (LibreOffice Impress, LibreOffice ๋๋ก์ฐ)
Open context menu - choose Arrange - Send to Back (LibreOffice Impress).