You're 'under no' (legal) 'obligation' to return the money. [=there is no law that requires you to return the money; you do not have to return the money]
The firm must fulfill its 'obligations' under the contract. = The firm must fulfill its contractual 'obligations'.
You can try the machine for free 'without obligation'. [=without being required to buy it or to do anything else]
(..) And we pray that you help sheldon get back on his rocker. Now,after a moment of silent meditation,I'm gonna end with "in jesus' name," but you two don't feel any obligation to join in. Unless,of course,the holy spirit moves you. Oh,my god,this is the best cobbler I've ever had. (..)2007 TvShow: The Big Bang Theory Title: The Luminous Fish Effect Season: 1 Episode 4