There is no issue to export org to latex pdf when "Body Only" is "off"

But, when "Body Only" is "on", the export is failed always.

Comparing "Body Only" on and off case, the on-case doesn't have
\documentclass or \usepackage headers. It looks it has only body and that's
why converting pdf fails always.

I can generate the "Body Only" "off" and modify the tex manually and
convert it pdf by manually via pdflatex, but it is tedious work.

Is there any way to fix this issue?