You can add custom fields to all documents at once while you’re importing. You can use this make some other notes about this batch of documents, such as tracking the source of each document in your set.
I’ll walk you through it.
First, add files as usual
Use the “Fields” interface to specify fields for these documents.
Now, every document you uploaded has the field values you wrote.
You can specify other field values whenever you add more documents to the document set.
The original documents’ fields will have the original values. The new documents’ fields will have the new values.
Export the document set, and you’ll see the field values for all documents.