Edit PDF in sharepoint online

For those hoping to see Acrobat at least be able to browse SharePoint so that you can open from/save to, there's a fundamental problem with that: Acrobat still doesn't support modern authentication, believe it or not:
https://acrobat.uservoice.com/forums/926557-adobe-acrobat-for-sharepoint-onedrive/suggestions/45249598-add-support-for-modern-authentication

So, if you "Apps that don't use modern authentication" blocked in your SPO Admin settings, as you should (but many probably still don't), when you go to add a SharePoint site to Acrobat it'll just sit there and not do it, leaving you confused. It's a sad state of affairs.