The short vertical and horizontal lines at corners

[guzhiling]

The short vertical and horizontal lines at corners

[yihui]

Those are crop marks. They are there to help with alignment when printing the PDF. If you are writing a book with Chapman & Hall/CRC, I don't think you should remove these marks. If you are not writing a book with them, I'm curious why you want to use their book style. Anyway, this task is beyond my LaTeX expertise, and I don't know how to remove these marks. If you have to, you will need to reach out to the help desk of the CRC press.

[guzhiling]

Thank you so much for your prompt reply! I am asking for someone who is working on a book with CRC, and the editor mentioned this. I would advise the author of the book to double check with the editor. Thanks!

[yihui]

Got you. In that case, there is nothing to worry about. The crop marks in the PDF are perfectly fine (I've published five books with them). The editor might be new to this job.

[guzhiling]

Got you. Thanks!