Which of the following is not an example of a red flag that would keep you from downloading an attachment

Answer:

The link contained in the email redirects you to a different site

Explanation:

This is not a red flag in the sense that, the ability of the link attached to the e-mail to re-direct you to another different site shows that it might be a phising message.

It is left for the person to re-verify and  decide if to go ahead to download it or not after it opens on a new site on the internet.

Answer:

  The attachment is a PDF file.

Explanation:

A link that causes an attachment to be downloaded and opened always presents a security risk. That risk is mitigated somewhat if you trust the sender to be security-conscious, and if you trust the target of the link to be free of malware.

So, a link with an untrusted source such as a company outsider, may present a security risk.

A message marked "urgent and time-sensitive" is employing "social engineering" to reduce your inhibitions against opening the link. That tends to be an indication that a security risk is involved.

A link that obscures the source of the attachment is less likely to be legitimate than one that is more transparent. That, too, is an indication of a security risk.

PDF files are traditionally considered to be safe document files that cannot execute code or introduce malware. This (the attachment is a PDF file) is likely the answer of choice.

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Comment on PDF files

The Adobe Acrobat PDF reader is known to have significant security risks, and hundreds of exploits are available to malware producers that will allow PDF files to introduce and execute unwanted code. There are alternative PDF readers with less vulnerability. And, there are file scanners available that can detect malware in PDF files.