Sumatra PDF is a slim, free, open-source PDF viewer for Windows. Sumatra has a minimalistic design. Simplicity has a higher priority than a lot of features. It’s small and starts up very fast. Options are a little thin on the ground but SumatraPDF provides a very comfortable environment for reading PDFs and you can print documents without much hassle. You can take this over Acrobat any day for looking at eBooks.