Is it safe to upgrade to El Capitan

Hi,

As long as you have a Time Machine backup or another backup system enabled you do not risk anything by upgrading to El Capitan. As long as the installation process goes smoothly, you will still be able to access your books. If you use older specific writing apps, you can make sure they are still compatible with El Capitan at https://roaringapps.com

Happy Upgrading

James

If you use your machine for serious work, you should never upgrade like that without having a bootable clone of your present system on a separate partition or drive, so you can quickly restore previous capabilities in case something essential does not work.