I use a whitelist

The vast amount of mail I get is first filtered on whitelist - anything not approved is thrown into a temp file. When I'm interested, I go through my temp file and filter on blacklist - anything from domains, countries and subjects that I do not approve of is deleted (and yes, Bangkok is on the list since none of my friends or acquaintances will ever write from there).

Whatever is left is usually spam, allowing me to refine my filter, or it is a message from some outfit I have not yet filtered, allowing me to choose whether to whitelist it, blacklist it, or ignore it.

PDF spam ? Pah ! If it's in the temp box, it can only be crud. All attachments are destroyed without even hesitating.