Edit PDF from shell as ODG

# Convert pdf to odg
libreoffice --headless --convert-to odg form.pdf

# extract odg to tmp folder
mkdir tmp
cd tmp
unzip ../form.odg

# edit content
vim content.xml

# repack odg
zip -r ../new_form.odg *
cd ../

# convert back to pdf
libreoffice --headless --convert-to pdf new_form.odg