macOS Preview function performance drop since update
The first thing to do is check on some common sense items:


Open Activity Monitor - is the system totally idle or 99% CPU used.
Open System Information (About this Mac) and check the storage - do any cleanup and if you are on a hard drive - consider freeing up 25% of the space to let the optimization run post OS upgrade.
Turn off automatic log in so that when you reboot your Mac - you get to choose which account to log in.
Open the Mac App Store app and apply all updates to Sierra.
After cleaning out CPU / Disk Space - boot to Recovery HD and let Disk Utility repair the Disk, then repair the Macintosh HD, then repair the disk one last time. If any errors are fixed, power down the Mac and start Recovery HD a second time and repeat until you have no errors detected to fix.
Now make a new user account and copy the files you’ll use to test to /Users/Shared - restart and log in to the new account and repeat the test for PDF.


This procedure is very general and catches 4/5 of the issues we have at work with our Mac. It’s not specific to preview, but will ensure you don’t look at a specific app when you actually have a system issue slowing down your Mac.