ColumnText

For more info about this example, read the answer to the question How to adapt the position of the first line in ColumnText?
In this example, we use ColumnText to add page numbers to an existing PDF document.
I'm converting a document which is created with a online editor. I need to be able to rotate the text using it's central point and not (0,0).
I have created rectangle using PdfContentByte . Now I want to add text inside this rectangle. How can I do this?