Thank you very much for the help. I realized that zoom was a problem only in one of my files (that I was reading at that moment).
The Kaffeine solution would help me a lot. I am searching for info on Kaffeine since you told. I installed it from: https://www.mobileread.com/forums/sho...d.php?t=151207
I can't get it work and I can't understand how I can make it show my own screensavers. I'm sorry, maybe it is an easy question, but can you give it a help? (maybe from private message, I don't want to burden here more).