No need to copy datafiles every time on standby database.
Jst use the following command on standby database.
1.select name from v$datafile;
2.It wil show unnamed file in the $oracle_home/dbs — location
3.then just use the following command
alter database create datafile ‘/dbs/unnamed.dbf’ as ‘/newname.dbf’ (Location of actual file on primary as well on standby database)
4.Now check select name from v$datafile;
Try this it will work in the Manual Standby Environment.