I have a money order I need to mail first class & was wondering if anyone knew if I could use printed DC on it? I'll include the additional $0.18 in stamps to cover it's cost, just wasn't sure if it was allowed according to USPS guidelines? Thanks!

I am not sure. Their website says "first-class parcels" http://www.usps.com/send/waystosendmail/extraservices/deliveryconfirmationservice.htm

Yeah, Thanks KJ!  I saw that too and then when I click on "First Class Parcels" I found this ::  First-Class Mail Letters – small rectangular mailpiece no thicker than ¼ inch weighing 3.5 ounces or less. Which is what I'll be mailing. Still wanting to double check though.

Delivery confirmation is not allowed on first class letters. You could send it as a parcel if you make it rigid and 1/4 inch thick or at least 3/4 inch thick. You will need to use the parcel chart to figure out the postage. Up to one ounce is $1.17 plus .18 cents for the DC. I would not use a standard envelope. They do not hold up well in the sorting process.