A tutorial is a method of transferring knowledge and may be used as a part of a learning process. More interactive and specific than a book or a lecture; a tutorial seeks to teach by example and supply the information to complete a certain task.
Tutorial
TL;DR: PDFs use complex binary/compressed data that standard text editors can’t read. To inspect the internal structure, use JPedal (for debugging content streams), RUPS... PDF stands for portable document format and is the world’s most popular file format. So it’s likely to be one that Java Developers need...