MuPDF - A Lightweight PDF, XPS and E-book viewer
MuPDF is a lightweight PDF, XPS, and E-book viewer. It renders text with metrics and spacing accurate to within fractions of a pixel for the highest fidelity in reproducing the look of a printed page on screen. It supports PDF 1.7 with transparency, encryption, hyperlinks, annotations, searching and more. The viewer is small, fast, yet complete. It supports many document formats, such as PDF, XPS, OpenXPS, CBZ, EPUB, and FictionBook 2. You can annotate PDF documents and fill out forms with the mobile viewers (this feature is coming soon to the desktop viewer as well).