If I own a C-corp or an S-corp in the US ( say for example Delaware ), and I take profits from revenue after expenses for the corporation and purchase stock in the US stock markets, bonds or other investment property without selling any of those investments purchased by the time of tax filing, would that reduce my corporation's total tax liability?
No, you cannot. Investment is not a tax-deductible expense.
Yes you can... By opening a pension fund and putting excess cash in there you can protect your cash. While the cash is in a protected pension fund. You can self-direct the funds activities or have someone do it for you. How ever you do have to make this fund available to all employees.