InDesign and Acrobat conflict
I just installed InDesign 2020 15.0. When I try to export a file to PDF I get an error message saying that file is already open, which it is not. Closing Adobe Acrobat and reopening doesn't solve issue, only restarting InDesign does. Hugely inconvenient. I have not been prompted to upgrade Acrobat and I never had that problem with earlier InDesign versions.
The issue was fixed in InDesign 2020 (v 15.1.2). The fix is also available in the latest release – InDesign 2021.
Please update to either of these newer versions of InDesign to get the fix.
Adobe InDesign team