As the original comment on the thread, which has received 1,926 votes to date, noted, SharePoint Server on-premises supported this feature "for some time." (Somewhat ironically, Microsoft officials tout how the subscription/online versions of Office apps get new features before the on-premises ones do.) More than a few of the nearly 200 commentators on the thread noted that the lack of this feature was a deal breaker for their organizations.
The problem was this: Whenever a customer needed to view or edit a PDF using Acrobat, the file first would have to be downloaded. But as part of a handful of new features announced last week, PDF files can now remain in-place within Office 365 in a customer's OneDrive or SharePoint document library. This means there's no risk of multiple, out-of-sync versions of files which a user needs to view, share or edit.