Dopus correctly open my password protected .rar archives. It ask me for password, but just once.
When i leave the folder/archive, exit the windows, then go back to my archive, i can enter again and no password is asked to me.
Is there any ways to "lock" the protected folder when leaving it or other option ?
Opus only caches passwords for about 2 minutes and never saves them to disk. If the password is remembered across Windows reboot then I suspect that either the archive isn't encrypted or you're not using Opus itself to view the archive.
(Or the archive has encrypted data but not not encrypted filenames and you haven't tried to read any of the data yet.)
WinRAR has its own (optional) password cache, so if you are opening the files in WinRAR rather than Opus then that may explain things.