Can I do yoga if I'm obese and not flexible?

Yes, most definitely one can do yoga, is a low impact form of exercise, and can be done with little equipment in the comfort of your own home. Exercise may not prove as beneficial as cardiovascular exercise, such as swimming, jogging, or cycling. 

Starting with basic yoga poses and movements will allow you and your body to slowly adjust to the new form of exercise. From there, you'll develop strenght, balance and endurance, and should be able to progress further from there. Coupling yoga with cardiovascular exercise on a different day will prove the most effective in helping you manage your weight. As the weight comes off, exercise, and yoga will become easier. 

Eating a health-balanced diet will best help you manage your weight by limiting the amount of sugar and carbohydrates that are consumed. With exercise, the weight should come down over a period of time.