As a C corporation, you will file a Form 1120 for the company's federal return, plus the applicable state corporate tax returns for the states in which the company operates.
If there was an S election made and the company is classified as an S corporation for tax purposes, you'd file a Form 1120S.
Forms 8K and 10K aren't tax-related forms. They are used by publicly traded companies to report certain financial results and significant events to shareholders.
