There are 2 types of PDF files. PDFs created by scanning applications use images, while PDF files created by software or printer drivers use text. SimpleIndex can read bar codes from either type of document.
With image PDFs, SimpleIndex will use normal image barcode recognition. With text PDFs, SimpleIndex can read the value of the barcode from text (if it was created with a font) or convert the PDF to an image and read it (if the bar code is an image).
To read the barcode from text is much faster and all versions of SimpleIndex include the ability to parse the text of PDF file.
Find out more about bar code scanning on our Bar Code Scanning Guide.