Slightly OT, but you would be surprised at how much power PDFs have (especially when opened in Adobe Acrobat/Reader). I recently came across this monstrosity[1] on HN, and the author mentions this:
> Scripts can supposedly do things like make arbitrary database connections, detect attached monitors, import external resources, and manipulate 3D objects.
That's an unprecedented level of power for what is supposedly a simple document format.
That being said, PDFs are only a threat when opened in a with support for these obscure APIs, such as Adobe's own readers. You (probably) will be fine opening untrusted PDFs in Chrome's PDF reader (PDFium) and Preview.