@h4rmony
I said it multiple times, "attacked by the ignorance" meant not necessarily security. It's ignorance of existence of free software often of superior quality for specific tasks. Just the phrase I quoted caught me there... Most of the time a text file, djvu or pdf file would be a better choice, attaching an Excel or a Word doc (or not being able to read say djvu) would be an ignorance in my mind.
the overwhelming majority of users wouldn't know what version of PDF standard a file attachment comes in.
For overwhelming majority internet and PC are a very dangerous place to be in already. I was simply arguing that if you use atril document viewer (like me) you're safer and more comfortable. The proprietary extension part of this file would not run, because it's not supported.
...because some versions of the standard are safer is wrong.
Once again, I meant the ISO open standard (versions <=1.7) Your allusion that it's a part of the ISO standard is wrong. A user is safer to use a free PDF viewer recognizing this standard and ignoring non-standard proprietary bits. I think I made it clear.