What are some alternatives?
FBReader - FBReader is an e-book reader for various platforms. Features:
Adobe Acrobat Reader DC - PDF Reader, PDF Viewer
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices
Evince - Evince is a document viewer for multiple document formats: PDF, Postscript, djvu, tiff, dvi, XPS...