Normally, that popup occurs if you aren't signed into your Adobe account.
For better or worse, running Adobe subscription applications do require that you are logged in with your Adobe account. You should click the Sign In button which will bring up a web browser window allowing you to login with your Adobe account. Once that is done, you should not be receiving that popup anymore. If you subsequently receive that popup, it might be indicative of some corruption of your software installation. You should then contact Adobe Customer Support (these communities are not Adobe Customer Support) by phone https://helpx.adobe.com/contact/phone.html and seek their assistance.
There is a more serious and widespread problem here, to do with something Adobe has altered that causes a purchased, registered and perfectly valid Acrobat X pro (part of CS6) to cease functioning.
Our Rotary Club's CS6 - purchased under the donations program in 2013. The other programs are functional but something is causing Acrobat Pro not to recognise the serial number any more, and not only demand that we "continue a trial" of 32,727 days - that we never signed up for - but since your last remote access attempt to fix this, Acrobat no longer stably opens a document - clicking "continue trial" just blitzes the program, so nothing is possible.
Two extended attempts at fixing the problem by remote access have failed, and a new serial number was promised just for Acrobat Pro - but this morning one of your staff claims that Adobe cannot fulfil the promise made - and makes no attempt to provide an actual solution but fobs the problem off to this forum.
After the Adobe message promising the new serial number was sent, there was a subsequent email from them telling me to use legacy files 1 and and 2 for CS6 (links provided) and do a complete uninstall and reinstall, but that's EXACTLY what Adobe did remotely on my desktop, and it not only did not work, but made things worse. Now, after that intervention, I can’t hit the “Continue Trial” buttton without zapping the document and crashing the program.
I’m desperate to get this fixed – it’s only nine days until the Rotary Youth Driver Awareness Day that I am organising, and I cannot even open the pdf questionnaire returned by the crash survivor, much less modify it as I need to do.