Hi Jeff,
I was able to reproduce the issue in your code. You need to add the footer distance explicitly in addition to your code to make the footer to display.
Here is a code snippet
//Add a section
IPDFSection section = document.AddSection();
//Set the footer distance
section.PageSetup.FooterDistance = 50f;
//Add the footer
IParagraph Footerpara=section.HeadersFooters.Footer.AddParagraph();
//Append the text.
Footerpara.AppendText("PageFooter").CharacterFormat.FontSize =20;
Here is a sample for your reference
DLSHeaderFooters.zip
Please take a look into it and let me know if you have any other queries.
Regards,
Dhivya.