I.R.I.S. Readiris Corporate 12 for Mac User Guide - Manual (Page 74)

Chapter 9 – Formatting and saving documents
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PDF Text
When you select PDF Text, Readiris recognizes text and creates
searchable PDF files.
The page image is not contained in these single-layered PDF files.
PDF Text-Image
When you select PDF Text-Image, Readiris recognizes text and
creates searchable PDF documents that contain the page image and
the recognized text.
The page image is contained beneath the text.
PDF Image
When you select PDF Image, Readiris generates image-only PDF
documents, it does not execute OCR.
PDF Image-Text
When you select PDF Image-Text, Readiris recognizes text and
creates searchable PDF files that contain the page image and the
recognized text.
The page image is placed on top of the text.
With this format you can always see the original document (as it
was scanned) while you are able to search for and copy-paste the
OCRed text, which is hidden beneath the image. As a result, this
format is useful for archiving purposes.
 When you are done selecting the options, click OK. Then click
Recognize+Save to recognize the document.