I formed an S-Corp in DE and have a NJ business address. I am not a store front and DO NOT collect sales tax. I provide a service and use a post office box as my address in NJ. What are my tax requirements? (i.e.) Which tax returns do I file? Do I file state returns with DE, NJ or both? Do I have to file annual reports? I have only provided services to companies located in PA. Do I have to file anything in PA? I have limited experience with this topic and could use all help possible. Thank you.

As a corporation, you have certain reporting requirements to BOTH states. You need to contact the state tax departments to determine what those requirements are.