mupdf is a lightweight PDF, CBZ, and XPS viewer and toolkit.

The renderer in MuPDF is tailored for high quality anti-aliased graphics.
MuPDF 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.

MuPDF is also small, fast, and yet complete. It supports PDF 1.7 with
transparency, encryption, hyperlinks, annotations, searching and more. It
also reads XPS and OpenXPS documents. MuPDF is written modularly, so
features can be added on by integrators if they so desire.