Sumatra PDF is a slim, free, open-source PDF viewer designed for portable use so you can easily run it from an external USB drive.It enables you to read and modify any PDF according to your demands.Sumatra perform the following functions: open PDF files via menu open PDF files via drag & drop page up and ´p´ for going to previous page page down and ´n´ for going to next page ´q´ to quit set different zoom levels via menu