Oops, I didn't mean to send this, and i can't delete it, sorry.

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...

Sorry, I'll try to clarify. I'm saving the pdf using Apache's PDFBox. XFA forms are saved inside the pdf and have an XML structure which consists mainly of a template section, a data section, and a form section which is the template and the data merged.. I can save the data part and Adobe reader will pick it up no problem. But the form uses this opening tag: . If that checksum is not valid, Adobe Reader will ignore that section. Since I'm modifying the contents inside the form tag, I need to upd...