Your PAB entries are stored in the o=pab branch of your
directory server (LDAP). If you configured an external LDAP or used the LDAP that comes packaged with NMS you
can either take full backups using db2bak or db2ldif, or you can just backup the o=pab branch using a command
similar to this
ldapsearch -T -b o=pab
-D "cn=Directory Manager"
-w directory_manager_password
objectclass=*
> pab.backup