PDF displaying comment symbols/icons on iPad

Hi everyone and thanks for being here!

I am a drafter using AutoCAD and I am providing a client with PDF files created using AutoCAD's built-in PDF maker. My client is viewing the PDF files on an iPad of some sort. His issue is that all of the text elements on the PDF are also showing a yellow icon which is getting in the way (see attached image)...

These icons do not appear when I view the PDF on my Windows 7 PC with Acrobat DC.

Can anyone please advise how to stop these appearing either in the printing phase or on the iPad?

Thanks in advance,

Hoffy