Choose Format - Arrange - Send to Back (LibreOfficeDev Writer, LibreOfficeDev Calc).
Choose Shape - Arrange - Send to Back (LibreOfficeDev Draw).
SHIFT+COMMANDCTRL+знак минус (LibreOfficeDev Impress, LibreOfficeDev Draw)
Open context menu - choose Arrange - Send to Back (LibreOfficeDev Impress).