When does a reader extension become a PDF reader?

by Jason Farrar article title Why PDF readers don’t seem to be an all-or-nothing proposition article by Alex Stott article title PDF reader extensions don’t make sense, says David Gifford article by Michael Witherington article title The short answer to the question “when does a PDF read a pdf” article by Adam Hockley article title You don’t need to have Adobe Reader installed to use a PDF viewer article by Dan M. Lee article title What you should know about Adobe Reader 4.0 article by Tom Kowalski article title Adobe Reader is just like Adobe Reader 5, says Joe D’Agostino article title How to use Adobe Reader’s PDF reader extension article by Joe D. Lee, Michael Wetherington, and Tom K.K.