How to add a content (html) with in thread or post

hi all,
i researching to add a content (a some sentences ) with in thread , this is automatic in addon .
who can help me?
i reviewed html bbcode, however it not as i hope.
a addon help me
- Can add a content(html) in Admin
- If user add a new post, content(html) will be display in bottom position of paragraph as image "Everthing is possible"