Acrobat Reader shows white box and no way to close it.

[ls_rbls]

Most likely you'll get some valuable assistance here in the user-to-user support forums too. And in other very frequent occasions Adobe employees will jump in and help and assits Adobe customers here in these forums.

But To get help from Adobe you must contact Adobe Customre Service directly. Try here: 

• https://www.adobe.com/about-adobe/contact.html#

However, see if this tip helps: https://helpx.adobe.com/x-productkb/global/unable-to-accept-end-user-license.html

I think the white box that you're seeing is related to the EndUser License Agreement dialogue window.

Since you cannot see the content via GUI close the Adobe Reader DC program and use Finder to navigate to this folder (as indicated in the link above):

• ~/Library/Application Support/Adobe/OOBE/

[ls_rbls]

Also, see these valuebale tips and troubleshooting tools:

https://community.adobe.com/t5/acrobat/acrobat-keeps-asking-to-sign-in/td-p/11525698?page=1