The enrichment mode works in two steps. In the first step, you scan the documents and their metadata from the document management system with the appropriate migration-center scanner. migration-center will store the metadata of all scanned objects in its database.
Each scanned record has a unique identifier in the migration-center database, called ID-in-source-system. For an OpenText Documentum source system, the ID-in-source-system would be the r_object_id of the documents.
In the second step, you export the additional data from the third-party system into a CSV file and scan this file with the new CSV scanner in enrichment mode. You have to specify the ID of the scan run from step 1 in the settings of the scanner. The migration-center will then check if the ID-in-source-system of a scanned record from the CSV file matches any ID-in-source-system in the specified scan run. If yes, it will add the data from the CSV file as additional source attributes to the existing record in the scan run. If not, it will simply ignore the record. The result will be a consolidated record in the migration-center database, as shown in the figure below.
Of course, you can repeat the second step several times, in case you need to consolidate data from more than one additional system.