A file should be saved automatically to cloud and only cache be saved in the device and also an option for offline saving should be provided to read offline. But basically saving to cloud will let you to acces the pdf from any device.And simultaneously refresh of history on all the linked devices and websites.
All the device should work as one rather than different it is ultimately same application opened by same people then, why extra effort in different devices.
This will allow user to download previously opened pdf anytime, anywhere and no matter how much we delete the app or close the page i can access my file in quick.

Where your able multiple account. In my case I had main account my wife's make an account and what a difference documents that we both needed for the same situation and I have to log out of each one and go to each one save each document After I filled and everything just to make it less of a hassle I would suggest the ability to just sync multiple account at least two. Or maybe it's someone forgot the login information for one of the account so they made a new one but with all the same information besides the email address make it to where they're able to add their account to that account without so much of a hassle just to get a PDF document because its already filled out but just cant log into that account.

I need to be able to create forms on the go on my android and ios devices. currently I can only do this on a Mac or PC. If a form is meant to be mobile, and it needs created or edited, this is not an option on mobile. While on the road, I do not always have access to desktop and need to be able to add radio buttons, text boxes, signature placeholders, and other form features. Please make the full-featured Acrobat Pro DC available on mobile. Reader is not enough. Even if you can interact with the forms, not being able to create or edit forms on mobile devices is less than ideal.