

Like the other products on the market, it has strengths and weaknesses. No, I'm not a Kofax fanboy, if I was I wouldn't have mentioned competitive products however, I am very familiar with it. It has a significant chunk of the document scanning market share. Kofax is used in enterprise-grade systems for scanning and automatic capture of millions and millions of documents a year. In addition it is highly customizable and comes in a variety of flavors with lots of add-on modules so one customer's Kofax system can be significantly different from other systems. Kofax has historically been sold through a system of Value Added Resellers so the quality of various implementations can vary widely.
OPEN SOURCE SCANNER CAPTURE SOFTWARE SOFTWARE
Most vendors are moving away from dongles to control the volume and are moving to software licensing.

It is possible, although much less common to have a one-time volume that doesn't automatically renew and when it runs out you would be required to purchase additional volume. Thus, you don't pay strictly "per page" in the sense that if you purchase a capacity of 1M images per year and you only end up scanning 500K pages you don't get a refund. 1M pages a year - auto renewing each year without additional cost). Typically the volume renews at the end of the term (i.e. Most of the scanning software vendors do use a "volume" or "capacity" license. I don't know of any open source solutions for scanning but I haven't ever really searched for any either.

Nearly all of these solutions have COM/ActiveX API support. Many document management solutions also have built-in scanning front ends but they're typically not as functional as the specialized capture products. To name just a few other vendors/products in addition to Kofax: Those requirements are pretty trivial for a vendor that specializes in scanning.
OPEN SOURCE SCANNER CAPTURE SOFTWARE PDF
There are many vendors of scanning products that can do what you want - scan, index, generate PDF with OCR overlay (personally, I prefer OCR underlay in a PDF).
