Thanks for the good tips on solving this one
I have also tried to find good solutions multiple times over the years but failed to be totally happy with the end results. I have full Adobe CS -suite and once again spent this morning trying to figure out how to use tools I have with Applescript to get job done and failed. As I am not willing to install Office suite so had to try something Else.
Tried again with pandoc, but could not figure out how to get all required components/fonts? installed for making it work with all different docx files people keep sending me. Some of them will give problems with fonts or something else that tex/latex software-sculpture do not know how to handle, so failed again with that.
After seeking third party converters for the task, I found this very automation friendly cloud service https://cloudconvert.com. It supports Dropbox folder triggers out of the box that allows you to simply drop annoying docx, pptx … files to folder for conversion. It also has nice CLI interface for shell scripting usage not to mention rich API for web-service purposes.
It is paid service with multiple options how to pay for each conversion. I chose 500 minutes prepaid package at the cost of 7€ (exl tax) that will allow me to do about 500 conversions. There is also free tier of 25 conversions, but it lacks the Dropbox folder watch that I wanted to have.
For me this will do the task. Hazel will now take all docx and pptx -files from my Download folder to conversion folder and return them once converted back in more usable format.