Migrating from a pfile to a spfile is really simple. You can use the following command on the console:

CREATE SPFILE FROM PFILE = 'C:\oradata\mydb\init.ora' 

... of course you have to enter the right path to the init.ora file...

To do it the other way is also possible, just type

CREATE PFILE = 'C:\oradata\mydb\init.ora' FROM SPFILE = 'C:\oradata\mydb\spfilemydb.ORA';