Do I need to remove backer board before laying carpet?"

1. if you plan on moving within a few years... it will be cheaper for you to take the short cut and level the Backer Board... put a good pad down (2lb) and your carpet. 2. if you want to live here for some time do it right and pull the the bb up... Strip it down to the frame adn lay a new subfloor down and adjust to the same height as the floor you are not removing... Some helpfull tools if you are doing it the right way: A good recip saw... not craftsman or ryobi.... buy a milwaukee or bosch... recip saw blades... milwaukee makes blades for this... almost look like a grinding stone at blade tip. buy some good sledge hammers and pry bars... the reason I say good... you can shop at HOme depot and buy an 8 lb sledge for either 12 or 25 dollars... the 25 has a shock obsorber in the handle... spend the money save your hands.  more