The personal note on org document

Question

I would like to put some notes on org document which should not be printed/ exported to pdf . Is it possible?

Answer 1

See the manual: C-hig (org)Comment lines

Lines starting with zero or more whitespace characters followed by one # and a whitespace are treated as comments and, as such, are not exported.

Likewise, regions surrounded by #+BEGIN_COMMENT ... #+END_COMMENT are not exported.

Finally, a COMMENT keyword at the beginning of an entry, but after any other keyword or priority cookie, comments out the entire subtree. In this case, the subtree is not exported and no code block within it is executed either¹. The command below helps changing the comment status of a headline.

C-c; - Toggle the COMMENT keyword at the beginning of an entry.

¹ For a less drastic behavior, consider using a select tag (see Export settings) instead.

Answer 2

You can exclude a headline from export using the exclude tag settings. By default any headline tagged noexport will be excluded, but this can be changed by setting org-export-exclude-tags. This variable can be set per-file using the #+EXCLUDE_TAGS keyword.