Adobe is currently testing a modified PDF online sharing feature with some users.
The current version is described on a web page:
On another web page the new variant is described:
The file to be share is uploaded to the Document Cloud and a link to the file is sent to the recipients by e-mail. Acrobat/Reader is no longer required to view and insert comments. All you need is a standard Internet browser. Recipients do not need an account in the Document Cloud either.
However, some definitions in print production files (overprint, transparency) are not displayed correctly by the Document Cloud Viewer. Therefore, caution is advised when using the Share function for approving demanding print production files!