Typically, this is caused by certain web browsers not rendering the PDF fonts correctly. Letters are omitted or too close together making it appear words are misspelled or missing. These errors are not actually present in the book.
If you download the file rather than preview it in the browser's window the issue will resolve. We also highly recommend using Adobe Acrobat Reader to view the PDFs. It is a free download you can find here: https://get.adobe.com/reader/Read more