How to manipulate a Check box in Word with Java and save as PDF?

I need to edit some Check-Boxes in a big Wordfile (docx) and save this then as PDF. This file contains many images and is about 19MB big. Maybe there will be the need of adding some Checkbox and text.

My idea was to use docx4j, but before to learn the ropes I want to ask if this is possible and which is the best way.

May it be better to save the document as a PDF and then use this as base for processing?

Thx for giving me some possible ways.