how do i upload multiple files and eventually download it after submitting in the summary interface

If your save target, ri!Electronic_File_Processing.attachment1, is not set up to handle an array of document IDs (which i'm guessing it isn't), uploading multiple files will not work.

Generally I'd suggest an approach where you instead have the upload field save into a separate variable i.e. ri!fileUploadList, where the type is document and it's set as an array.  Then afterwards in your process model you can handle mapping these ids to different members of a CDT array, particularly if you're faced with the task of creating a new/blank row in that CDT for each document that was uploaded.

If your save target, ri!Electronic_File_Processing.attachment1, is not set up to handle an array of document IDs (which i'm guessing it isn't), uploading multiple files will not work.

Generally I'd suggest an approach where you instead have the upload field save into a separate variable i.e. ri!fileUploadList, where the type is document and it's set as an array.  Then afterwards in your process model you can handle mapping these ids to different members of a CDT array, particularly if you're faced with the task of creating a new/blank row in that CDT for each document that was uploaded.