Thanks Kosta, Yes, I checked those sites but there's no useful info :(.
I can write xfa data with pdfbox, I'm actually using it because iText
didn't work well for some forms. I can manually write the xfa data and
it works perfectly, but the algorithm for calculating the checksum for
the tag doesn't seem to be documented, There's even a
stackoverflow question about this subject from iText's creator, but no
reply:
https://stackoverflow.com/questions/27470442/how-to-calculate-the-checksum-in-an-xf...