You could do this if you wanted. Due to the amount of words plus limited ability in formatting, we highly recommend using a Word Processing program. A couple of suggestions are Microsoft Word or Google Docs.
Be sure to setup the margins in your file if working with a word processing program.
One you have wrote your book, you should of course save it with the default file type. Then you click save as and choose save as a PDF.
Please see this article about converting a PDF or .doc file to .epub or .kpf format if you want to make an ebook.