From Qoppa Software:
jPDFFields for Linux is a Java library to work with interactive PDF forms in both AcroForm and XFA formats. jPDFFields for Linux allows your application to get and set field values and can also import and export to FDF, XFDF and XDP formats. Additionally, jPDFFields can also flatten fields in a document. Flattening is the process of merging the fields into the PDF content layer so that the information is retained but as static PDF content.