I am looking for a lightweight file browser for my Android 2.2 device. I used Astro File Manager before, but it looks like it has expanded with a lot of features, and does not fit on the limited space I have left.

Basically I am looking for an app that

* Runs smoothly on Android 2.2
* Not occupying tons of space (few MBs only)
* Provides a file browser, and options to open files from there.
* Less is more, as basic as it can get without losing functionality
* Is gratis

My main use of the app would be to browse some folder containing some PDFs. I do not need anything fancy. Can you recommend such an app?