Awful. upgraded to 1499 a month and STILL cant combine files. Terrible product
It sounds like you’ve subscribed to Acrobat Pro. If you are still using Adobe Reader, you won’t see the combine features.
Instead, try downloading and installing Acrobat from this link instead: https://documentcloud.adobe.com/link/appcenter/
Additional help can be found at https://helpx.adobe.com/download-install/kb/download-install-acrobat-subscription.html