Unable to save to a vault from Adobe Acrobat

If you try to "save as" to a vault via Adobe Acrobat you can't save it. You don't get an error, but it just won't work. It looks like this is something that was recently introduced.

As a workaround you need to turn off the Protected Mode in Adobe Acrobat DC:

• go to Edit > Preferences > Security (Enhanced) and then uncheck Enable Protected Mode at startup