There is a walktrough widget (https://magicbox.imejl.sk/walkthrough/), however you need to save a site in html format to sdcard then you can open it with widgets in-game. I think you could use it to open manuals in-game. I just tried to save a random Doom manual and open it with Walktrough widget, it opened perfectly. So you need a .html file to be able to use Walktrough widget. I don’t know if there’s a another way, probably yes but I’m not a expert.