Some recent announcements will make it much easier to work with PDFs protected with sensitivity labels. Adobe is now bundling the MIP plug-in with the Acrobat installer and has plans to allow users to apply sensitivity labels within Acrobat. But the big news is the change in Office applications to generate protected PDFs when saving, exporting, or sharing protected documents, spreadsheets, and presentations.
The Microsoft-Adobe initiative to support Azure Information Protection for PDF files has reached general availability. Things look good and the issues encountered in the preview are removed. You can store protected PDFs inside Office 365, but be prepared to download the files to be able to view them.