My office is in an office complex where the front doors of two businesses face each other and share the same lobby. Both businesses have glass windows and doors and reception desks that face each other. Whenever I go through the doors I feel like I should smile at the receptionist or raise my hand in a greeting type fashion because she has no where else to look but directly at the person exiting the office. Should I introduce myself or wave or just continue to pretend like I don't see her?

I would guess, normally she is busy and does not have time to wave at anyone that happens to be coming in and out of your office.

You could stop once, and introduce yourself, but it is not really needed.