Convert Non-Container Oracle DB to Container DB
Here are the two situations:
There is no direct way to convert a Non-Container 12C database to Container 12C database. All you can do is to consider Non-Container database as a pluggable database(PDB) and attach it to the existing 12C container database.
With that said - How to create a PDB Using a Non-CDB?
Both the CDB and the non-CDB must be running Oracle Database 12c Release 1 (126.96.36.199) or later.
If your current non-CDB uses an Oracle Database release before Oracle Database 12c Release 1 (188.8.131.52), then you must upgrade the non-CDB to Oracle Database 12C.
Once you have both your Non-Container database and Container database running on 12C,
When transporting a non-CDB from an Oracle Database 11g Release 2 (184.108.40.206) or later Oracle Database 11g database to Oracle Database 12c, the VERSION Data Pump export parameter must be set to 220.127.116.11.0 or higher.