: Supports over 80 file types and includes professional measurement and markup capabilities.
Sometimes, you don't even need a downloaded .exe. If you have an internet connection, a web-based acts as a portable solution without the USB stick.
: While not a traditional "exe" file, the Autodesk Viewer is arguably the most portable option since it runs entirely in a web browser.
If your favorite viewer isn’t portable, use or VMware ThinApp to repackage it into a single .exe that runs from USB. But for most users – just pick from the 5 above.