Yes, you need a software license to protect you from any liabilities, specifically when you use proprietary software because it’s intellectual property. The software license outlines a list of responsibilities between the owner of a product and its end-user. The license will outline a set of rules that you should follow to avoid a violation of its use.
The software owner also grants you the rights to use his program, but you can’t access its source code since it’s a Closed Source. If you use copyrighted Open Source software, you must affix a copyright notice to your written code to protect yourself unless it’s on a public software repository like GitHub.