I think you are right. Various users have various needs and preferences. The best option would be to let each one decide what he wants and what is best for him. But I think that DcUpdater can already do that, doesn't it?

In general I prefer to do updates manually (I like to see what has changed in the program) or to be notified (only notified, no download, no installation) that an update is available.

A good place to start is this:

http://www.techsupportalert.com/best-free-non-adobe-pdf-reader.htm

I have no experience other pdf file readers, but you could try those mentioned there, to see if you like one of them.