First up, Edge now supports the EPUB file format, so you can read any unprotected e-book in the file format just like you can with PDFs. While reading EPUB files, Edge lets you change the text size and font, and choose between three themes (light, sepia, and dark). You can also leave bookmarks, use the table of contents or seek bar at the bottom of the browser, search for words or phrases, and use Cortana to define specific words.
Edge launched with Windows 10 and is not available in the earlier and better versions of Windows, so this feature won't be coming to most Windows users, but we do have other options.
Most web browsers have one or more plugins or extensions which can read ebooks. Chrome has Readium, for example, among other apps. Firefox has similar web apps, and of course one could always use Google Play Books to read an Epub in your browser (but it might not be worth effort of uploading the ebook before downloading it).
image by zoovroo