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xfa forms - checksum for the <form> tag

ferrarimartin
Level 1
Level 1

Hello,

    This question has been asked before, but I cannot find an answer anywhere.

    For XFA forms, adobe reader adds a checksum in the <form> tag when saving. I'm trying to automatically fill an xfa form, and I need to calculate that checksum. Is there any documentation about how to perform that calculation?

Thanks,

     Martín.

0 Replies
Kosta_Prokopiu1
Employee
Employee
Not sure I understand what you mean with checksum in the Form tag. Are you saving the data or the whole PDF? How did you find that checksum? Are the PDF reader extended? What has the "automatic fill" of an xfa form to do with that checksum and how do you fill the form?
ferrarimartin
Level 1
Level 1
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: <form xmlns="http://www.xfa.org/schema/xfa-form/2.8/" checksum="igN4bJAPtFedO8QmvxpYOT1U9p8=">. 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 update the checksum, but I cannot find the algorithm for doing that.
Kosta_Prokopiu1
Employee
Employee

Oh I see. I am not sure that PDFBox can write XFA data. This checksum must be created by the manipulating software and uses certain parts of the XFA section. I cannot tell you which ones and how you would calculate that. I collected a number of links that might help you:

 

https://kbdeveloper.qoppa.com/fill-populate-xfa-dynamic-form-with-field-data-in-java/
https://kb.itextpdf.com/home/it7kb/examples/xfa-examples
https://stackoverflow.com/questions/33088789/how-to-use-itext-to-fill-out-dynamic-xfa-pdf-from-data-...

http://www.lawandsoftware.com/blog/filling-xfa-pdf-forms-using-pdfbox/

 

ferrarimartin
Level 1
Level 1

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 <form> 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-xfa-form

    Oh, and just to clarify, this is the tag I'm referring to:

 

<form xmlns="http://www.xfa.org/schema/xfa-form/2.8/" checksum="vFVrmhPyTqaed06K/Kz2KSlTWbQ=">

....

</form>

Thanks again,

     Martín.

ferrarimartin
Level 1
Level 1

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