By default, when your TiddlyWiki document is posted on-line anyone can read it, and they can edit it, and download it (with any changes they've made), but they can't *save* it on-line unless you've installed specific scripts on the server or are using hosting such as GitHub Pages... and even then, they'd need your ID and Password / OAuth / AccessToken, which is only stored in *your* browser (using Local Storage), which permits *you* to save changes online without re-entering your ID and PW, but won't let anyone else save online.
Note: Inside TiddlyWiki also has a custom-built "locked/unlock" toggle that, by default, hides the admin/editing functions to give a simplified "read-only" experience; however, even when "unlocked", visitors cannot *save* back to the online copy.
-e