Dimitris, thank you for the question.
CA Test Data Management (TDM) is a well formed application for anonymizing the regulated or sensitive fields in copies of production data so it may be used in Development or Test without risk of in appropriate exposure. It is designed to act on known data, using the copybook that applies to it, to apply masking to the regulated or sensitive fields to achieve anonymization.
CA Data Content Discovery is designed to scan for regulated or sensitive data anywhere it may reside in mainframe data stores, without the need of identifying the associated copybook. It is used to find regulated or sensitive data in datasets that may be lost, orphaned, abandoned, or even maliciously hidden on the mainframe, so discovered data can be appropriately protected, archived, or deleted.