Hi, so Aptos is a font?
Can you check from your font folder if Aptos is a Type1 font? Adobe is not supporting this type of font anymore.
from the Microsoft site it looks like it is a TrueType Font Aptos - Typography | Microsoft Learn so you should be ok.
Can you run a test? Type some text in MS Word and format it with variations of Aptos (bold, italic...) and export to PDF using the same process as you used in Outlook. Let us know if you get the same error. This is to check if it is an Outlook issue.
Next from Outlook, can you try to File > Print > using PDF printer (instead of export) to check if you get the same issue?
Lastly, is you MS Office up to date? (File > Account > Updates)
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