The app supports a long list of formats, so you can open any document with any of the following extensions: .odt, .odp, .ods, .ots, .ott, .otp, .docx, .pptx, .xlsx, .dotx, .xltx, .ppsx, .doc, .ppt, .xls, .dot, .xlt, .pps. This means you can open any document created with OpenOffice or Microsoft Office.
LibreOffice Viewer is a good text editor that's continually under development and being improved. Even though its features are a bit limited right now, the number of different formats it supports makes it an app to keep in mind for all those who frequently use text documents on Android.
Requires Android 4.0 or higher