This looked interesting:

You Can Now Markup and Modify PDFs in Google Drive Using Adobe Acrobat – Review Geek

but I had to reach about two plus warning pages about possible dire consequences (my words) allowing 3rd party apps permission. I can't recall jumping through this many hoops before but rarely do I install 3rd party apps so perhaps this has become the norm. Anyone using this without their tin hats on?

Third-party sites & apps with access to your account - Google Account Help