Hi Eric,
Thank you for your update,
We can add the barcode after conversion of Html to pdf.
PdfCode39Barcode barcode = new PdfCode39Barcode();
// Setting height of the barcode
barcode.BarHeight = 45;
barcode.Text = "CODE39$";
Please find attached sample project.
Please let us know if you need further assistance.
With Regards,
Praveen