There have been some reports of difficulty installing the ArcGIS Maps for Adobe Creative Cloud extension, so I'd like to try to clarify a couple of things and offer some potential troubleshooting steps.
Typically, the extension should be installed through the Adobe Add-ons site. In the past, Adobe has used a product called Extension Manager to manage the installation/uninstallation of third party extensions for its Creative Cloud platform applications. However, this application has been deprecated and should no longer be used. Installing through the Add-Ons site can sometimes fail though, usually with an unhelpful error. If you've tried the troubleshooting steps here and are still having issues, then you may want to try a third party extension installer.
We've had good success using the Anastasiy Extension Manager. To use it, you first need to download the .zxp file for our app. You must be signed in with your Adobe ID to proceed. Click the blue 'Download ArcGIS Maps for Adobe Creative Cloud' button, ignore the other inaccurate steps about using Adobe Extension Manager. Then open Anastasiy's Extension Manager, click File-->Install Extension and browse to the zxp file.
Please note that the above steps will only work if you have a Personal Adobe ID. If you have an Enterprise ID, the downloaded .zxp will not install correctly. If you have an Enterprise ID please contact Esri Technical Support for a copy of the .zxp that will work with your account.