Q: We evaluated PDFTron PDF to PDF/A document conversion and it works great 
We have additional requirement to generate PDF document from URL. Does PDFNet or any other your product support generating PDF document from URL?
A: You can use PDFNet SDK (http://www.pdftron.com/pdfnet/features.html) to generate PDF from URL and for PDF/A validation/conversion (among other things).
As a starting point please take a look at Html2Pdf sample project:
‘pdftron.PDF.Html2Pdf’ (http://www.pdftron.com/pdfnet/html/classpdftron_1_1PDF_1_1HTML2PDF.html) is part of PDFNet Convert Add-on. You can convert Web sites to PDF via URL, load local HTML files, or convert HTML strings (e.g. dynamic content) to PDF. You will need to download the extra DLL from http://www.pdftron.com/pdfnet/downloads.html. All of this is described as part of the above sample.
With respect to PDF/A support please take a look at PDF/A sample project:
PDF/A conversion is part of PDFNet PDF/A Add-on.