It will definitely not be stamped such as to make the content unusable. Instead, there will be a code on each and every page which can be used to trace the product back to which customer bought it in the first place.

There has been least one instance (that I'm aware of) where a pirate went through the effort of erasing the watermark on every single one of 200+ pages before putting it online. Then again, there have been examples of DRM getting cracked as well. Watermarking has definitely proven to be a lot more palatable to customers though, and it's definitely an option Denny should seriously consider for his own online store.