A program to convert files

https://pandoc.org/installing.html

For example, it can covert .html to .md:

Win+R cmd

cd desktop
pandoc 1.html -f html -t commonmark --wrap=preserve -o 1.md

So with this program you can save (Ctrl+S, only HTML) an article from some site, remove everything extra from HTML and convert it to MD, which you can upload on your site.