When Adobe invents PDF format and encourages people to use this format, the reference is available for free. Now you can also download this document from Adobe website. As a result, there are so many PDF related products around the market.
After trying some of PDF readers, I go back to Adobe’s Acrobat Reader. Although this free reader is large and feature-limited, it is official and user-friendly. Don’t say Foxit is small, it is no longer free (I hate those evaluation marks).
So now I switch to Tracker Software Products’ PDF-XChange Viewer which is free and powerful. It contains important features that only available in Adobe Acrobat Standard/Professional, such as commenting and editing. I finally find I can mark the PDF books to insert comments.
The only issue I see is that PDF-XChange Viewer icon. That icon is so complex that seems ugly IMHO. I prefer a much simpler and clearer icon. That’s why I think Adobe Reader wins.
BTW, future version of PDF-XChange Viewer may support Ribbon UI. So let’s see how a free PDF viewer (and simple editor) can evolve (hope it does not follow Foxit).