To add keywords and a description to the stored files (see manual Add Files (to Samples, Customers, Orders)) or to link them to additional customers/orders or samples, go to Navigation bar -> Settings -> Stored Files. There you can delete the files with or add more information by clicking on Details.

File Detail View

You can add a description to the file and make it more easily searchable with keywords, as well as link additional customers, orders, and samples where this file should appear.
Additionally, you have the option to display this file to the selected customer in their customer zone by activating the checkbox Share file for customer zone. (Note: if no customer is selected, this file will appear for all customers in their customer zones).