I have Acrobat Pro DC as part of a Creative Cloud subscription. Running on MacBook Pro under OS X High Sierra 10.13.6.
For several weeks I've had the issue that when starting the app, usually by opening a PDF, there is a interval of a minute or more when it is unresponsive. The document is slow to appear. The Mac process indicator appears (spinning rainbow disc). The delay is quite aggravating. It only happens on the first document opened in a session.
If I quit the app and reopen it, the same thing occurs.
This behavior started recently; and the app never had this stuck period during start-up.
It is not appear to be dependent on having an internet connection.

I won't speculate on mechanism. Just wish it would get remedied.

Acrobat Pro DC 2019.10.20098
Architecture: x86_64
Build: 19.10.20098.316574
AGM: 4.30.84
CoolType: 5.14.5
JP2K: 1.2.2.42832