Here's the list of things I do when troubleshooting a slow computer:
1) Run a malwarebytes scan and remove anything found
2) Install all applicable driver updates
3) Run "sfc /scannow" from an elevated command prompt
4) Install all applicable Windows updates
5) Install all applicable Office updates, if installed separately (true for some versions of Office 2016)
6) Check amount of free disk space (ideally at least 20 GB free)
7) Check for adware/crapware that is installed. Remove by normal add/remove programs
8) Check CPU usage and disk usage for conditions above 99%
