After some attemps, Iīm going to answer some of my own questions (if it helps to someone):
1. I have found an old jailbreak version (0.10.N) for my firmware, so I havenīt had to update it. It was in a russian web. If someone needs this old jailbreak version, just ask me for it.
2. I did the jailbreak at my own risk (I didnīt know if my Kindle had the jailbreak or not). I still have a Kindle, not a beautiful 9,7" brick
3. Yes. At least, it works for me.
It worked perfectly in my x32 W10 PC, but I had a problem during the process installing in my x64 W10 PC: it didnīt detect the Kindle while it was using the usbnetwork. Happily, I found this:
https://www.mobileread.com/forums/sho...86&postcount=1
After installing the driver, my PC detected perfectly the Kindle.
Although the refresh of the eink display is some delayed, it isnīt a problem for me when I use MS Word, so Iīm satisfied.