Merging two PDFs with form fields results in a PDF with empty fields.
The issue seems to be similar to
PDFBOX-1031, but in my case i see the fields but not the value in the fields.
I use the following command to merge the PDFs:
java -classpath pdfbox-app-1.6.0.jar org.apache.pdfbox.PDFMerger a.pdf b.pdf c.pdf