Painful feet and toes are listed as a side effect and should be reported to your doctor.
From their website:
Coumadin side effects
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects:
skin changes or discoloration anywhere on your body;

purple toes or fingers;

pain in your stomach, back, or sides;

low fever, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);

diarrhea, fever, chills, body aches, flu symptoms;

easy bruising or bleeding that will not stop;

blood in your urine;

black, bloody, or tarry stools;

nosebleeds, bleeding gums, coughing up blood;

feeling weak or light-headed;

sudden headache, confusion, problems with vision, speech, or balance;

sudden leg or foot pain; or

sudden numbness or weakness, especially on one side of the body.

Less serious side effects may include:

nausea, vomiting, stomach pain;

gas and bloating; or

hair loss.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.