In a statement released by Dropbox, “We want you to be able to collaborate with PDF files on Dropbox in as few steps, clicks, or swipes as possible. Ultimately, we want you to be able to work with any kind of file easily, from viewing to editing to sharing. Our collaboration with Adobe, the inventor of the PDF, is the next step in this process.”
Given that these are also files that are being edited/modified within Dropbox, the changes you make to them will be synced across all your Dropbox accounts and shared files/folders. This will allow for better collaboration of PDF files using Dropbox and Acrobat. This new feature/collaboration will work across the desktop version of Dropbox and the mobile version as well.
However for now it seems that the functionality will go live on the desktop version first, and it is expected that iOS integration will be coming in the next few months. As for Android users, it looks like you guys can expect the feature only in 2016.