The problem with splitting the table into two tables is how do you enforce the PK on both tables.

First, you need to figure out how to identify the "old" records. Usually, this is done with some sort of DATE field. Once this has been determined, I would use this as my primary partition key.

Assuming doc_type is of some importance, I would then create a partitioned global index using doc_type as the partition key along with any other attributes you need.

Lastly, I would create single PK with a regular index. This way, your PK will still be enforced, you can have "old" data in a read-only tablespace, and "active" data in a read-write tablespace. Just remember to keep your PK in a read-write tablespace and rebuild it whenever you split or move partitions.