If you are looking for free, legal books to put on a 10-year-old Red Tiger player, your best sources are:
Back in the mid-to-late 2000s and early 2010s, these "unbranded" or "import" MP4 players flooded the market. They were famous for being affordable alternatives to the iPod Nano, often featuring FM radios, voice recording, and the ability to read .txt files—which is likely what the "txt free" part of your search refers to. ss nina 10 yrs red tiger mini mp4 txt free
High-quality formatting, though you will still need to download the text-only versions. If you are looking for free, legal books