What do these strange icons mean in PDF?

[TREMAiNE]

I sent a document off for something I am working on, the person I sent it to has sent it back and its now showing some speech bubble icons on the PDF file:



They appear to be interactive, backed up my the person I sent to has sent it back saying ".....-just clarified a couple of points on the questions..." and there being no other changes to my document, though I can't find a way to interact with them and have no idea why they're there.

[DrTre]

Comment fields but perhaps you need to update your reader

[TREMAiNE]

Yup, that was it!

Cheers!