Yes, I know about them and always prove extremely useful every time I receive a file with a wrong/no extension and have little clue about its content. But since the question was about how OP could work with “files with extensions” produced in Windows, I wanted to help clarify what are they, why they are used and that files do not need to be converted or whatever to be opened in Linux as it can “work with them” just fine.
For the #4, the file extension can be seen just as a note, a little tag that’ll help you (or anyone else that will receive your file) remember which program you should use to successfully open the file.
From the viewpoint of your computer, in fact, a file is just a sequence of bits and every program can open every file, only it will not be able to find what it expects and actually do something useful with it, just as you can open a book written in any possible language: in most cases you will unable to undestand it, in some others you will be able to read it without any problem.
The “concept” of extensions was than introduced to allow your file manager (Explorer for Windows, Finder for macOS, Dolphin for KDE or Nautilus for GNOME) to know which program to launch when you double click on a certain file through a simple association table (that you can edit in your system preferences).
In regards to Linux you can sometimes read that file extensions are not a thing, but this is just because in the commandline you launch a specific program that you personally point to a certain file, so there is no file manager that needs to guess which app should be launched to open the document you just double clicked on.
That said, I think that should be pretty clear that in a Desktop context (like in a Personal Computer) that double click on a file situation pretty much applies to Linux too, so extensions will be useful and respected by the file manager you’ll find installed in your distro of choice, even if it can use other means when that is missing.
This argument reminds me of the Tolerance Paradox described by Karl Popper, who stated that in order to maintain a tolerant society, the society must retain the right to be intolerant of intolerance.
In the licensing context, yes, the Apache and Expat licenses may grant your users the freedom to create proprietary software out of your works, but at the cost of sacrificing all the basic freedoms of all the users that will use the derived non-free product.
So, like Popper said that you should prefer removing the “smaller” freedom for a society of being intolerant in order to guarantee the “greater” one of remaining tolerant in the future, since you still have to choose which freedoms you are going to negate, it’s preferable to use copyleft and impede the “smaller” freedom of creating proprietary software than not using it and allowing the crushing of future users’ fundamental rights.
Yeah, it’s easies and will make your life simpler as long as you want to do something the producer contemplated. As soon as you need a feature that is a little bit more peculiar, good luck with that.
And with this i don’t mean that Android is perfect, just that an even more closed ecosystem isn’t exactely the best choice.