One year ago, I have written a FOSS tutorial on writing webapps on Go and published it via Leanpub using pay what you want model, the gitbooks version gets 1.5k readers each month ~50 unique per day and 1k downloads per month. only 4-5 users have paid $ via leanpub, I was thinking of removing the pdf version from gitbooks and making leanpub version as paid only. Is it amoral to start charging $ for PDF version? the source is FOSS on github and always will be OSS.edit: https://github.com/thewhitetulip/web-dev-golang-anti-textbook/ is the link.