What you want to do is scan the book in using Optical Character Recognition (OCR). You could scan each page and run it through software yourself, but that is a lot of work! I recommend hiring an OCR scanning service that will do it for you. The google search phrase to find a service is “OCR scanning service” – I don’t have any specific companies to recommend so I’d start off by looking local to see if you can keep your money in your own community.
Depending on the service or software that you use, you may have to clean up the document afterwards, but I’d recommend that anyway since there are very few books in the world without a typo so it’s probably worth updating anyway.
There are a few other methods you could use, such as scanning the pages in and setting up a task for typing each page out to Amazon Mechanical Turk, which may or may not help keep your costs down and accuracy up, but I personally wouldn’t use that method as I’d still be the one that has to manually scan each page.