I.R.I.S. Readiris 14 for Windows User Guide - Manual (Page 146)

Readiris TM 14 – User Guide
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Readiris can generate a separate output file for each document. This
avoids your having to scan only one document at a time.
Example
Let's say you're scanning a stack of 30 pages. The first 10 pages
belong to Document 1, pages 11 to 20 belong to Document 2 and
pages 21 to 30 belong to Document 3. If you indicate that your
stack of paper in fact contains 3 documents, Readiris will generate 3
separate output files.
How to separate paper documents
With Readiris, there are 2 ways in to separate paper documents.
You can do this by means of:

blank pages
In this case you simply put a blank page between two sheets of
paper to indicate where the new document begins.

cover pages containing a barcode
In this case you can, for instance, put a barcode sticker on each
first page of a document.
To access the document separation options:

Click the Readiris button, and then click Advanced Settings.

Click the Document Processing tab.