Files by Google made its debut a couple of years back, and Google has slowly been adding features to it. The latest additions in v1.0.33 include a PDF viewer and the ability to adjust playback speed for videos.
The new features are pretty straightforward. The PDF viewer acts exactly as you'd expect; it lets you view PDFs. The playback speed adjustment lets you swipe the speed from 0.5x to 2.0x at increments of 0.1, though most people will probably just use the 0.5, 0.8, 1.0, 1.5, and 2.0 buttons at the bottom.
These features are bundled in Files by Google 1.0.33, which is live on the Play Store now. If you can't get 1.0.33 through the Play Store for whatever reason, we also have the APK over at APK Mirror.