Why does Stack Overflow scan your resume for viruses?

PDFs have been a major malware vector.

Any file uploaded should be scanned especially when you are uploading something which is then downloadable by someone else such as this example.

Yes, because there are ways to trigger a malware install or Viruses using a PDF files.

Example:

* https://www.welivesecurity.com/2018/05/15/tale-two-zero-days... (a remote-code execution vulnerability in Adobe Reader and a privilege escalation vulnerability in Microsoft Windows triggered via PDF)

* https://blogs.quickheal.com/beware-pdf-attachments-launching... (PDF's launching Android Malware)

* https://www.sans.org/security-resources/malwarefaq/pdf-overv... (A slightly dated FAQ on PDF Malware)