Just adding a little more meat to the answer. The solution ended up being found by researching what methods worked with a PdfTemplate which is what a PdfImportedPage is derived from. I've added a little more to show how it interacts with the rest of the document being built up. I hope this helps someone else.
internal static void InsertPDF( PdfWriter writer, Document document, Section section, Byte[] pdf )
{
Paragraph para = new Paragraph();
// Add note to show blank page is intentional
para.Add( new Phrase( "PDF follows on the next page.", <your font> ) );
section.Add( para );
// Need to update the document so we render this page.
document.Add( section );
PdfReader reader = new PdfReader( pdf );
PdfContentByte pcb = writer.DirectContentUnder;
Int32 pages = planreader.NumberOfPages;
for ( Int32 pagenum = 1; pagenum <= pages; pagenum++ )
{
document.NewPage();
PdfImportedPage page = writer.GetImportedPage( reader, pagenum );
// Render their page in our document.
pcb.AddTemplate( page, 0, 0 );
}
}