Hi raymondl18653947,
In Acrobat, you can choose File > Open from Acrobat.com to open the PDF file that you've stored in your Acrobat.com online account. When you save the file with your markups, choose File > Save to Acrobat.com to save the file back up to the cloud.
So, you will be marking up the PDF offline, but it's easy to access and save your stored files via Acrobat.
Best,
Sara