Business Corporate Tax Return (1065, 1120S, 1120) - ENGAGE CPAs

A business or corporate tax return is filed every year to report a partnership, S-Corporation or C-Corporation's income for a period of time. Usually the prior calendar year.
If you own a partnership or S-Corporation, you have a separate business tax filing requirement, every year, even though no tax is actually paid at the business level, it's all personal income tax to the owners. The owner's share of the profits to be taxed show up on Schedule K-1 which is produced within the 1065 or 1120S and is used to report income on the individual owner's tax return.
A return is due to be filed every year by March 15th. Similar to the individual tax return, every business can extend their tax filing by 6-months. But keep in mind that if you own a partnership or S-Corporation you'll need to file your 1065 or 1120S to get your K-1 before you can file your 1040.
If you own a C-Corporation, you have a separate business tax filing requirement, every year, and you do pay tax at the business level. A C-Corporation is the only business entity that needs to pay a business tax at the corporate level. All other tax is paid at the individual level.
The C-Corporation return is Form 1120 and it is due to be filed by April 15th, if you're a calendar year-end filer. C-Corporations do have the option to extend the return for 6-months.
These returns are important to save in your own files and folders, in your Dropbox, iCloud, etc. You should have this on hand should anyone request it. And you should also have copies of all tax documents that you received and workpapers and emails that were used to prepare your tax return. You should keep these records and receipts for atleast 7 years should they ever be subject to an audit.