Rendering the document to an image and using OCR on it would bypass a lot of trouble trying to make sense of the source, wouldn't it?
The basic issue imho is that NLP algorithms are very inaccurate even with perfect input. E.g. even with perfect input, they're maybe only 75% accurate. And even an a text-processing algorithm that's like 99.9% accurate will yield input to your NLP algorithms that's like 50% accurate, so any results will be mostly unusable.