This project hasn't changed for five years and there is no short/mid term improvements scheduled.
I believe tesseract remains a reference open source engine (there are few in that field). There is an exe for tesseract https://code.google.com/p/tesseract-ocr/downloads/list
So you can also easily write a commandline using the commandline service of Nuxeo Platform and then call this commandline from a work that will be ran asynchroneously.
One of the challenges is to know what you want to do with the ocr: decorate the pdf (you might need to use pdfbox lib), display it in overlay in a custom UI, etc..
