You cannot protect a file against other users who have root access.
If you encrypt a file on another machine where you are the only root user and upload it to that shared machine, then the content of the file is safe from the other roots. However, as soon as you decrypt the file on the shared machine, it is no longer confidential. Other roots can snoop on your password and record it, can copy the data as soon as you decrypt it, etc.
If you want to protect the file from other users who do not have root access, then file permissions are sufficient:
chmod go= somefile makes the file inaccessible to anyone but its owner. If you make a directory inaccessible to someone, then they can't access files inside that directory either. Encryption is not useful.
Storing an encrypted file on a machine and decrypting it on that same machine is only useful to protect against one specific threat: a leak of the disk contents (either because the disk is stolen, or because a backup is stolen). Encrypting files does not protect against attackers with purely software access.