This post talks about what is an STP file and how you can open such files in Windows 11/10. STP or STEP is a 3D assembly file saved in Standard for the Exchange of Product Data (STEP) format.

I want to do some very basic editing of STEP files, e.g.: I need to do this sort of thing about a hundred times, so I'd rather learn how to fish than pay someone to do it, even if it's only a few $$ ...

Usually, there are dedicated applications to view different types of files. However, if you are looking for a viewer that lets you view files of multiple types, you have landed on the correct article.