This is described in Chapter 5 iText In Action, 2nd ed . All sample code is available online. In particular, MovieCountries1 and MovieHistory2 deal with page headers and footers.
It comes down to using the PdfPageEvent implementation (usually derived from the PdfPageEventHelper to shorten the template) to draw in the direct content of the page during the EndPage event (or BeginPage, I suppose).
You need to know where you want, and you must draw with an instance of PdfContentByte , so you cannot use the Paragraph / Chapter / Chunk / Image / etc classes at a high level. You have to draw this over there, draw here. ColumnText may help a little ... but only for plain text. Everything that is even remotely fantastic, and you yourself.