I used a trial version of Acrobat Pro XI which expired so had to purchased subscription to DC, but do not like DC and want to run XI instead. Can I do that? And how?

With the permanent license you couldn't, but I hear that this is possible with subscriptions. I cannot confirm it, it would be good if you let us know if it works. I believe the key is to use the Creative Cloud app, which has a section for licensing older versions.