Revert to an older version of PDF in Acrobat Document Cloud

The best way is to go to your computer's backup and retrieve an older version of this file. That of course asumes that you create regular backups. If you don't then this should be a wakeup call to start doing that. 

If you never did a "Save As" on this file, you may be able to recover a previous version using a binary editor. Before you start, make a copy of your file and only work with that copy, never touch the original file, unless you want to risk to destroy the file even more.

You need a binary editor to do this, Wordpad or Notepad will not work. I use vi on a Mac in binary mode for jobs like this. A PDF file is saved by adding an incremental update to the file. This means that when you start to search backwardsmfron the end of the file, you might be able to find the previous end of file mark. Look for %%EOF - one you find it, remove anything after the %%EOF and save your file. You might be able to recover the previous version of the file this way. I wrote about this a few years ago: http://khkonsulting.com/2017/10/pdf-time-machine/