You can check to see if password file exists in the following directory:

/ORACLE_HOME/Ora81/Database/PWDsid.ora

Create a password file with ORAPWD utility found in ORACLE_HOME/Ora81/bin using following syntax:

C:\> ORAPWD FILE=PWDSID.ORA PASSWORD=PASSWORD ENTRIES=MAX_USERS

Hope this helps or for more info read Oradoc.