如何自动填写XFA（PDF）表格？

I'm looking for a free option to fill a XFA PDF form. I know that iText is an option but their commercial prices are too expensive for me, I'd prefer something fully open-source. There is PDFBox but it doesn't seem to allow for inserting data into XFA forms, or at least there's very little explaining how to.I'm looking for a free option to fill a XFA PDF