This is a well known method for creating counterfeit USD. I do not know how the method works exactly, but you are supposed to 'bleach' a 5 dollar bill and print a new bill ($100 for example) onto it. The bill will pass some tests like the marker test, since you are using genuine paper. It will still retain some characteristics of a $5 bill such as the watermark, so you should be careful if it is going to be inspected when you spend it.
I have only seen counterfeits being sold by a few people. Send me a PM if you need help finding a seller.