SumatraPDF reader
GPL-3.0 License
SumatraPDF is a multi-format (PDF, EPUB, MOBI, CBZ, CBR, FB2, CHM, XPS, DjVu) reader for Windows under (A)GPLv3 license, with some code under BSD license (see AUTHORS).
More Information:
books pdf
CAJ 转 PDF 转换器(GUI 版本)
PDFium - Project to compile PDFium library to multiple platforms.
Lightweight PDF viewer
A Gtk/Qt front-end to tesseract-ocr.