One big file will cause problems and even non opening in some older readers. Most people split at each chapter to avoid these problems and to make it easier to resolve problems while editing, so you only work on one chapter at a time in search and replace.
You may have other weird problems because when you press the space bar you insert a non breaking space, which means as far as the reader is concerned, the two words are one for the purpose of display. You can only get rid of this in book view searching for and replacing it with a press of the spacebar in codeview.
You probably need to check out
http://www.w3schools.com/ and look up anything there you don't understand in code view. Save your mess with another file name, then go in and remove any formatting that doesn't make sense to you. It can take some time if you converted a pdf file to get this.
Orwell is out of copyright probably only in Canada and Australia, so don't figure on distributing them elsewhere.