I've seen people make their own books in PDF files, get paid by PayPal, and sell them on their personal homepages. In the case I saw it, it was a bit like progr

I've seen people make their own books in PDF files, get paid by PayPal, and sell them on their personal homepages. In the case I saw it, it was a bit like programming or Arduino examples. If it's not at the platform level, but very small, I think you can do this, but reselling will be a little more complicated.