Can a woman return to work before going to her postpartum appointment?

Possible. Some pregnancies are very uncomplicated and depending upon the woman's general health, stamina, and abilities and the requirements of the work place, she may be able to return to work. This would require a discussion with her obstetrician, her employer, hr, and consideration of child bonding and care. This should all be discussed prior to delivery with all concerned and very carefully.
Best to wait. Your postpartum appointment is set for the best period of time to recover from birth. In general for your well being and for the best bonding with your baby, it is good to take the time off unless there are compelling reasons not to do so. If you must return to work, you are entitled to accommodations such as time to pump breast milk, rest periods, avoidance of heavy lifting and no stress.