Don't know if its legit or not, but its a scam like the "get paid to stuff envelopes thing" you won't make anything unless the person you send the letter to buys whatever it is your advertising and then maybe.
If you send the same letter/message/advertisement or whatever to more peoples you don't know, it's called a SPAM ! You can now guess - spamming is legal or not ?
Without details none of us can say, but as donlin says above "make money stuffing envelopes at home" is a pretty common scam. See more info from the FTC: http://www.ftc.gov/opa/2002/12/richmond.shtm A snippet from that case: Here are a couple of other similar scams: http://www.ftc.gov/opa/2007/09/envelopescheme.shtm http://www.ftc.gov/opa/2006/06/sunray.shtm http://www.ftc.gov/bcp/edu/pubs/consumer/invest/inv14.shtm