What are some alternatives?
When comparing calibre and PDF-XChange Viewer, you can also consider the following products
FBReader - FBReader is an e-book reader for various platforms. Features:
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices
PDF Reader X - PDF Reader X is a nest in the class PDF reader, PDF annotator and PDF editor for the Mac OS X operating systems.