I would not recommend using Adobe tools, I'm sure the output will be bloated and slow and not Pi friendly. Probably expensive as well.
Forget about the Windows 10 thing. At least for now it has no graphics at all.
So what to do?
I think at this point perhaps you should tell us the nature of your flash content. As it's concerned with literacy I could guess it's fairly simple "slide shows" of pictures and words, maybe with some multiple choice questions and such.
If we knew a bit about the content and it complexity perhaps we could come up with suitable solutions. Is there an example we could see on the net?
Is it really necessary that this be used with a browser at all? Could an application on the Pi do the job? There seem to be lot's of graphical programs available that might be useful.
Whatever solution it will take work on your part to create it for the Pi. But if you have all the text, pictures and other assets already it may not be such a big job.
Edit: In terms of HTML5 technology there are libraries available that make using HTML5 canvas and such things much easier. For example this looks nice: http://fabricjs.com/
and is exactly designed to do a lot of what FLASH does. I have no idea how well it might perform on a Pi. You only have to visit that page from a Pi to find out I guess.
Memory in C++ is a leaky abstraction .