Sumatra PDF Portable is obviously the portable version of the very popular Sumatra PDF. It is a freeware pdf application.
Here are some screenshots to illustrate the features and user interface of this application:
Sumatra PDF Portable: Fast PDF opener. Screenshot of Sumatra PDF Portable - 1144px · 985pxFreeware PDF reader also supporting CBZ, ePub, CHM. Screenshot of Sumatra PDF Portable - 1144px · 985pxSumatra PDF Portable: User interface. Screenshot of Sumatra PDF Portable - 1144px · 985pxScreenshot of Sumatra PDF Portable - Size: 1144px · 985px