Hi philk32438964 ,
You might need to open the PDF in Acrobat and run the Preflight tool to embed missing fonts.
Please refer to this KB article : https://helpx.adobe.com/acrobat/using/analyzing-documents-preflight-tool-acrobat.html
This may be completely off track, but I will mention it because people do sometimes end up on the wrong path. Proofreaders do not in general edit text at all, they return the marked up file for editing. It's often vital to do it that way, because if you edit the PDF there is no way to get those edits back into the original file, for future updates.
Also, the chances of a successful edit to a TeX produced file of any complexity is negligible. PDF is not for that.