Output JSON of word template
To be honest, I’m not sure that I understand your desired scenario right. There’s the conversion API which describes rules and examples of conversation process: ONLYOFFICE Api Documentation - Conversion API
I believe it’s useful if you want to convert a file with Document server. But there’s no support for docx\json conversion.
If you run Document Builder, probably this title will be fruitful: ONLYOFFICE Api Documentation - ONLYOFFICE Document Builder integration API
As you see, you have to use CDocBuilder.SaveFile method in case of changing file format output result. But format types don’t support json format too: ONLYOFFICE Api Documentation - ONLYOFFICE Document Builder integration API
If I misunderstood the situation, please provide us with details and your exact desired scenario.