The textbook for Engineering3 is distributed as an ebook. Here is a snippet from the textbook so the ebook format can be explored, and users can get a look at the structure of the Modules. Note how there is a drop down table of contents that brings users to module index pages, and from the index pages users can link to the sub sections. Users may also use the full table of contents page to link to any part of the text (only Module 4 is active in this snippet).
There are search and bookmark features, and a built in annotation tool that allows for adding answers direct to the pages. Have a look at the textbook sample here.