Can't see the comments made by someone else on the PDF

Received a PDF from a another user, when I open the document can see the yellow colour highlighted sentences and the comment bubble. When I move the curse, can't seems to opent he comemments or not apeparing. Read through many comments here, but still failed to open the comments. User who sent me told me he saved as usually doess.

This is a quite a important document and with many comemnts to reviewe. Please assist me on this matter.