If you are one who likes it, this Apple Support Communities user tip explains how you can keep it.On February 25, 2014, a critical security flaw was corrected in all versions of 10.9 with the 10.9.2 update (earlier versions of Mac OS X are unaffected): 10.9.2 Combo.Software tested before that date may not work with the operating system. issues have been reported on Apple Support Communities.
Note, download times may be longer than usual on first release.
Backup (link explains how) your data before you install anything.
Just because you've seen an issue which appears on a bulletin board, or is reported to you by a friend in a Mac OS X update, it does not mean the update is itself bad.
A mathematical improbability exists to test all combinations of software and hardware compatible with Macs.
They recommend using the Print window's built-in PDF - Mail PDF function when you go to print a PDF.
You should really at least backup everything to two separate destinations that are not touched by the computer before upgrading or until after the upgrade is complete. Printer and scanner driver issues with Yosemite are covered with more details on my Mac OS X printers page.
Do not trust those reports, until those reports are published after the official release of Sierra.
Apple may elect to change features at the last second, as it has done on countless operating system improvements before.
There are also issues with signatures not working at all in Mac OS X Mail.