SumatraPDF is, first of all, a viewer for different kinds of documents. Luckily, in spite of its name, it supports opening not only PDF but also other formats for which it is sometimes difficult to find a viewer, such as ePub, Mobi, XPS, DjVu, CHM, CBZ and CBR. The application is characterized by loading and opening documents very fast with a low consumption of system resources. As some other similar tools, this one lets you install plugins to view documents without ever leaving your browser, and fortunately, such popular Internet navigators as Opera, Firefox, and Chrome are supported.
The program’s interface is quite simple, with a toolbar and a few buttons to customize the way documents are shown. In this regard, you can view them both in single or two-page view, as well as adjust zoom level. Likewise, there is the possibility of sending a specific file as an email attachment.
I understand this tool is meant to be fast and light, and probably because of that, it does not have as many features as other PDF viewers. Regrettably then, you cannot use it to set bookmarks or any other of file navigation signaling. Likewise, it does not allow making annotations, let alone editing any part of a document.
In a nutshell, SumatraPDF has the main advantage of being lightning fast and available at no cost. Luckily, there is a portable version available, which you can take with you on a USB drive. As reported above, users expecting more than viewing documents can be a little disappointed with the lack of other features.