Explanation
The main migration tool for migrating to ADB is Data Pump. You can export your schemas and import them into ADB using Data Pump. To sync up the additional/incremental changes on the source database during the export/import process you can use GoldenGate or GoldenGate Cloud Service to replicate those changes to ADB.
In the current release you cannot use physical migration methods like backup/restore. Data Guard, database clones, and transportable tablespaces to move your existing database to ADB.
https://www.oracle.com/database/technologies/datawarehouse-bigdata/adb-faqs.html#MIGRATION