I recently made the switch from iText to PDFBox and ran into a similar issue. I asked this question and eventually worked out what I needed to do to generate reports with an unknown number of pages.
This model works well for generating reports containing lines of data generated from a ResultSet...though that's the only way I've been using it thus far. I may run into limitations, but for now, it's getting the job done.
And I guess I should state that I am still laying out each page manually, but this method does at least generate my pages dynamically depending on the number of results that return.