轉正是要向外貼找人廣告的, 因為要公平競爭,不可黑箱作業.

If the company wants to convert you, then HR need publish this AD position in company web site.
However, internally, they all knew this position is open for you ONLY.
You can apply the position after you see the job AD.
In normal case, your manager will let you know ans ask you to apply this position from company web site.
Enjoy holiday!