We do have a license for NReco for PDF generation. Now we have a requirement for updating the form fields in the PDF dynamically through dot net code, do we have support for this in NReco? if not any free library alternative for PDF form filling as we cant invest again in license? Ours is a .Net based MVC web application. We were using iTextSharp earlier but iTextSharp is EOL, and has been replaced by iText 7. We can't buy the license for iText 7 now.
NReco.PdfGenerator is just a wrapper for wkhtmltopdf tool; it is only about HTML-to-PDF conversion. Wkhtmltopdf cannot modify existing PDF files at all.
To fill the PDF (and, possibly, then 'flatten' it) you can use iTextSharp 4.1.6 which is licensed under LGPL and can be used for free. It has number of forks that are maintained and .NET Core compatible, for example this one: https://github.com/VahidN/iTextSharp.LGPLv2.Core