I installed coolreader, and the librerator fork.
Pdf reading was fine (I didn't find the options I was searching for: something to manually define a "grid" of margin/border to make the software use the whole screen for text, plus the letters were blurry every two lines).
Then the software has started to do strange things, like launch himself randomly at startup, or ignoring my will to close it. After one reboot, my kindle was bricked, I used the fastboot/imx_usb_loader to fix it.
Everything works fine at the moment.