LibreOffice is an open source office suite for Windows, OSX, Linux, and now Android. Earlier this year Collabora and the The Document Foundation (the non-profit which supports LibreOffice) announced the development of a version of LibreOffice for Android. That very early release was buggy and unstable, and most importantly it lacked any way to actually edit files.
But development continued, and now the latest beta release supports editing documents. It also works a little better.
It still offers a far from complete suite of features and the tool can't actually create a document from scratch, but if you download the latest development build you will find the app added some editing options to Writer, Calc, Draw, and Impress, including basic copy and past of text and images and simple text formatting (bold, italic, underline, and strikethrough).
The app also features support for opening and saving a broad range of office formats, including MS Office as well as Open Office formats (which are also used as the native for mat for LibreOffice).
The interface has also been optimized for touchscreens in general and Android in particular, which in part explains why the feature set is so limited; designing a touch interface for something as complex as an office suite is not a simple task.
that difficulty is part of the reason why Andropen Office, the Android port of Apache Open Office, still uses a desktop interface.
Andropen Office has been under development since 2013. I haven't used it recently, but given how long it has been under development I would try this app first. It is going to be more functional and stable, and if nothing else, Andropen still looks like it is designed to work with a keyboard and mouse rather than a touchscreen. If I did a lot of office work on Android, I would be using those peripherals.