A couple of comments on the Reader thread.
Yes, it is possible to choose the level of a created PDF, but many
people just use the default.
Until quite recently, I never had a problem opening PDFs with Acrobat
5 (just the message warnignof possible loss of features). These days I
often come across PDFs that Acrobat 5 reckons are broken and
unreadable, so I suspect the culprit is probably Acrobat 9 (possibly
also 8).
I have yet to find a "broken" PDF that Foxit Reader has a problem
with, so I would endorse a previous recommendation to use this, as it
is also faster and less bloated than current versions of Acrobat Reader.