OCR software that won't alter the original PDF image?

I have a great number of PDFs of older type-written documents that I need to keep the original image of but want to make them text searchable (OCR). I have tried Adobe's Pro's OCR option but it has a problem recognizing the word spacing from typewriters and keeps chopping up words. I also tried ReadIris but it creates a new image of the PDF with a more 'readable' text in place of what was in the original document. I couldn't find a way to change this, either. Is anyone aware of a good OCR program that will keep the original PDF image but can make it text searchable?