You used the phrase "PA as resident Corp with income from outside."

Your corporation did no business in PA? And you stated this is IL services, but there are some States with sales taxes for specific services rendered remotely.

You have to look up if there is sales tax nexus, if there is simply a corporate filing report for PA or it's more than this, and other details for everything you are asking. No one person bothers to know everything, and requirements change.

Here's a place to start:

https://mburrkeim.com/tax-forms/pennsylvania-tax-forms/