Where orphan pages should be placed to serve?

Hey there. I need to some pages be served under my domain, like: myhugosite.com/sale-festival.html, which is a one-page landing page, with a completely different structure, but using same assets.

where should I put it to work?

I mean my Hugo blog is on myhugosite.com and now I want to have some fully HTML page be up under myhugosite.com/A, myhugosite.com/B, … .

Static pages go under the root of your /content/ folder in your Hugo project. The filename is used to generate the URL by default and the file format can be either .md or .html