Hi Acro88,
As I understand the issue from the description mentioned above, pdfs are taking long time to open and close, could you try following troubleshooting steps:
1- Check if an update is available for Acrobat using "check for updates" option under Help menu, rebooting the machine and check.
2- If that doesn't work, go to Edit > Preferences > Go to the "Documents" category. Set the number of files in the recently used list to 1 (this will remove all your files that you have recently used from that list). If this fixes your problem, then there may be something wrong with one of the files that you've recently used (e.g. a network drive no longer being available).
3- If step 2 doesn't work, try turning off your virus and malware protection and try again.
4- If that doesn't work, go to Edit > Preferences > "Security (Enhanced)" category and set "Protected View" to "Off" and uncheck "Enable Enhanced Security" > click OK, relaunch Acrobat and check.
Please note: disabling protected view and enhanced security is for troubleshooting purpose only, and not recommended. Please turn the feature back on after troubleshooting is complete.
Let us know if you need any help.
Shivam