Under `File extension names` in the Automation file uploads section in Security Center, you see the pdf file extension. What does this indicate?

Answer options:

A.PDF documents will be ignored by automated investigations
B.PDF documents will always trigger an automated investigation
C.PDF attachments will be sent to the cloud for additional inspection
D.PDF attachments will be blocked

Correct Answer: C 
Enabling the content analysis capability makes sure that files and email attachments can automatically be uploaded to the cloud for additional inspection in Automated investigation. Hence, only option C is correct.
Option A, C and D are incorrect as pdf file extension in auto file doesn’t block pdf files or trigger any automated soc investigations
Reference: 

https://docs.microsoft.com/en-us/microsoft-365/security/defender-endpoint/manage-automation-file-uploads?view=o365-worldwide