A free program for Android, by South Pole Mobile.

This app is a complete package for viewing, reading, editing, creating, and saving all documents on your Android device. It includes PDF, DOC, DOCX, XLS, XLSX, PPT, PPTX, TXT, ODT, RTF, FB2, ODP, and a few other file formats. It’s a very easy-to-use app with a user-friendly interface and supports offline viewing. It has built-in editing tools, like add text, highlight, and strike through, and you can even use the toolbox to add shapes, text, and other objects to your document. It also provides a spell-checker, a grammar-checker, and a few other tools that will help you to write and edit your document with ease. You can also use it to create PDFs from your documents.