Just asked: my client is placing comments in Apples Preview.
That probably explains why comments are not transferred as expected.
Too bad Adobe is not working with 3rd parties to make sure this works as expected
(or 3rd parties not making sure their product is compliant with Adobe)!
Hi Paul,
so basically the workflow is:
You export to PDF from InDesign CC 2019.
Client opens PDF with Apple's Preview.
Client is doing comments with Apple's Preview.
At that stage you get the PDF back and you try to import the PDF to the PDF Comments panel.
That will totally fail like presented with reply #2 here.
Then you open the PDF in Acrobat Pro DC, latest version.
Some, not all, comments are missing perhaps due to commenting technology issues or incompatibilities in commenting systems of Apple's Preview app and Adobe Acrobat.
You save the PDF with a new name.
You can import the new PDF with InDesign's PDF Comments panel.
Regards,
Uwe