Sumatra PDF, also known simply as Sumatra, is a free, open source, lightweight PDF reader for Microsoft Windows, written by Krzysztof Kowalczyk.

The first version of Sumatra, designated version 0.1, was based on Xpdf 0.2 and was released on 1 June 2006. Version 1.0 was released on 17 November 2009 after more than three years of cumulative development.