Yes, obesity does cause foot pain and it does in a number of ways.
The extra weight that is carried simply puts more load and pressure on the foot, making almost every foot problem there is worse. This include conditions like plantar fasciitis, stress fractures and joint strains. Those who are obese also tend to have a problem with their feet swelling which can cause painful problems as the footwear become too tight.
Obesity also increases the risk for other problems that also affect the feet, such as osteoarthritis. This can affect all joints in the foot.
Those who are obese also can have a number of medical conditions, such as diabetes that can also affect the foot.