On Windows, Adobe Reader can export and view a list of comments through the Comment tab on the right side. On Linux, in Evince PDF viewer, the side pane has a drop-down annotations menu that lists comments. Press F9 key if you don’t see the left-hand panel.

One can extract all comments and annotations from a PDF file by

apt install texlive-latex-extra

pdfannotextractor --install

pdfannotextractor in.pdf

This yields a .pax file without plain text. However, it was not clear how to read this file.