Hi Jorrit,
According to your description, I have tested the issue from my side in PowerPoint 2016 for Mac 16.14 (Build 180610): File> Export…> Export as PDF.
And I cannot see the same behavior as you, all the sections including images, text, figure, icons, shapes and Chart in the presentation show normally and with high quality. (I open the PDF file in Preview.)
To better understand your situation, please confirm the information below:
1. Does this issue happen with all PowerPoint files? Even new file? Try to new a presentation and export to PDF.
2. Please provide your steps exporting PowerPoint file to PDF file, if necessary, please capture screenshots or record a video and send to us viaPrivate Message.
3. How do you open the PDF file? With which viewer?
4. Could you please capture a screenshot of the comparison before and after exporting?
In addition, for the “why do I bother to update my software?”, with each update, we push out security update, non-security update and feature update, the purpose of each update is to improve the product for end users.
So we are always suggesting users to update Office product to the latest version to get the latest features and security assurance.
Best Regards,
Gloria