hexapdf_test.rb

require 'hexapdf'

# Use local copy of http://foersom.com/net/HowTo/data/OoPdfFormExample.pdf
file = 'pdf_form_example.pdf'

doc = HexaPDF::Document.open(file)
page1 = doc.pages.first
widgets = page1[:Annots]&.filter{ |a| a[:Subtype] == :Widget }

# See what the widgets look like.
p widgets.map(&:form_field)
p widgets.map(&:form_field).map(&:concrete_field_type)

# Write some data into the form
given_name_text_box = widgets.first.form_field
given_name_text_box.field_value = "Daniel"

# Now save it
doc.write("test.pdf", validate: false, incremental: false, update_fields: true, optimize: false)