The shadow file is specifically designed to be read ONLY by root. The
point in this file is to prevent people from seeing your encrypted
passwords because there are commands like "crack" than can figure out
many passwords from their encrypted values. Prior to introduction of
the shadow file the encrypted passwords were stored in /etc/passwd and
if they weren't properly formed were very easy to break.
link
/etc/shadow file stores actual password in encrypted format for user's
account with additional properties related to user password i.e. it
stores secure user account information. All fields are separated by a
colon (:) symbol. It contains one entry per line for each user listed
in /etc/passwd file