Search for Project Gutenberg
You might have to create a Google Cloud file. Do this on a desktop.
My guess is it's an HTML file
If in doubt looke for an App reader for the extension you download
Be careful theres an imposter sight that looks like Project Gutenberg. Never give any personal info or register as a preferred user or premium user
Then with the ebook in google cloud folder use thr USB to drag and drop into your Documents folder on tablet