Comment You Need More than a Software Solution (Score 3, Insightful) 237
I don't think you can find a good solution just by technical means alone. Having run into this problem as a company attorney, I can say that the best defense is to define and enforce a strong document management policy. Technical solutions without a defined policy will only make you a pariah.
Also, you should check to see how the specs came to light in the document at issue. I recall one episode where one of our business development personnel sent a draft contract (in Word format) to a potential customer having used an earlier contract with another customer as a template. The BD person deleted the details from the earlier contract and inserted new (less favorable) terms. The other party turned on the redline mode to see the deletions and insertions and demanded the same terms as the earlier party. Everyone involved at our end was pretty embarrassed. The solution was to require than all drafts of all legal and business documents be sent in PDF or a "scrubbed" version of the Word document using a product from Workshare.