Just put it under the user directory and set the permission just like you we do Linux fs .
Using hadoop fs shell command.
hadoop fs -chown
Usage: hadoop fs -chmod
In addition for backup We can configure HDFS Snapshots point in time file recovery .
You can use Access Control List (ACL) to protect your file in HDFS. Pls refer the below links
Superuser(hdfs) can delete any file in hdfs. So all i need is to make an hdfs file that cannot be deleted by anyone even superuser like the way chattr command do in linux. With ACLs i cannot make a file undeletable for all users.