(configuration required: duplicat= false and archive activatedAs mentioned before, the Kepler - Attachment fields | simple & multiple custom field can be configured to store multiple files.
Step 1: Click on Attach files Icon 
and select files.
Step 2: Choose one, or multiple files from the opening window or, drag and drop your Files.
Step 3: At this step, you can:
...
Step 4: The Attach File Manager controls automatically the attachments according to the administrator's configuration, and displays error messages in case of files that do not correspond to the field configuration.
Case Case 1: Files extensions are different from the configuration.
Case 2: The sum of all sizes is greater than the defined one.
Case 3 : One or more attached file(s) is empty ( file size equals 0 KB) differently from the configuration.
