Can I protect a file that I share with a password?

Yes. When you click the Share button next to a file/folder and select Send Link, a new window pops-up. If you want to protect your shared file/folder with a password, tick the Link is unprotected checkbox. The password will appear next to Copy link to share. If you are sharing your file/folder using the Add People option, the content is already protected, because you need to have a registered Koofr account to access the file/folder that is shared this way.